Defeat the Rancor on Taris
Before the door leading into the room where the Rancor is standing there is a severed arm or a corpse, open it take the Datapad and Synthesized Odors, then go into the room, careful not to get too close to the Rancor as it will hunt you down and smash you with its enormous paws etc. and you will die almost instantly, instead go to the pile of corpses, and take whatever is inside (ah the life of the chosen one eh?) then open them again and place a Frag Grenade (you can do this by opening them then pressing 'X') after placing the grenade open them a place one of the odors that you took from the arm. The game will switch to a cinematic showing the Rancor running to the pile (with you safely back inside the doorway, picking up a corpse, eating it, then blowing up. hope this helps in your quest to save the galaxy. May the Force be with you.

Magic Healing:
Go to a area that is safe from combat (Not in combat or in a room) and pause and go to the map screen. Now hit the X button to jump back to the Ebon Hawk and be healed. Select Map again and hit X again to go back to where you where.

Experience Doubled
If you've discovered the secret bounty organization, then no doubt you will have been assigned a mission involving killing a slave trader named Zuulan as part of your initiation into the society.

When you find Zuulan's speeder, select the option which sets off his alarm. Zuulan and his thugs come running, and no matter what conversation option you choose, combat is the end result (remember that you MUST BE ALONE for these missions).

Instead of attacking your assailants, choose to "use" the speeder again, and this time select the option which affixes the frag mine to the hull of the craft. As a result of this, you will kill the Zuulan who comes running out to his speeder and gets blown away by your bomb, but at the same time, a second Zuulan and cronies is spawned very near by. Pick up the credits and equipment off of the dead Zuulan and then round the corner to engage in conversdation with the other Zuulan and kill him as well (an easy battle).

You'll get twice the stuff and twice the XP, plus if you're a light sided character who needs the credits, you don't gain the extra dark side points for killing him! It's a win-win situation.

Infinite Experience
In the dueling room on Korriban, there's a computer that lets you fight prisoners. Once you get your computer skill to the level that allows you to use 0 spikes to Hack Into Security Cameras or Hack Into Sith Database Files, just select that choice a few times and when you exit the computer interface, you'll get a load of experience.

Voice Change
With your primary controller plugged into the first port, plug a second controller into the fourth port. At any time, you can use the second controller to change the pitch of the voice acting.
Black Button: Lower pitch (Barry White)
White Button: High pitch (like Michael Jackson)

Watch Hidden Ending
Plug two controllers into your Xbox. Outside the doors to the final battle with Malak (don't open them!), push down both triggers and press the Y Button on both controllers at the same time. You'll need a third hand or a friend to pull this off.

Companion Killer
On Dantooine during your Jedi training you will be sent to investigate someDark power emanations in the wilderness. When you find Juhani, you can turn her to the Light Side and have her join your party, or you can threaten to kill her. Do so and you will set off an interesting chain of events that not only lose you Juhani as a party member (since she's dead) but sends another Jedi member towards the Dark Side.

Earn Different Endings
Finish game on the Light Side (by doing good deeds and denying the Dark Side) to see the Light Side ending. Finish game on the Dark Side (by doing evil and accepting the Dark path) to see the Dark Side ending.

Easy Heal
Anytime you are in a safe area (not in combat or inside a room) you can instantly heal yourself. Go to the Map screen in the pause menu and hit the X Button to instantly leap back to the Ebon Hawk. Your party members will be magically healed. You can then select the Map screen and hit X again to jump back to where you just were.

Extra Items
On the Ebon Hawk, talk to each member of your crew. You can ask each one to make you specific items:
Mission - Security Spike/Play Pazaak
Canderous - Arenal stimulants
HK-47 - Fighter simulation (shooting mini-game)
Jolee - Medpack
T3-M4 - Computer Spike
Zaalbar - Grenades
Juhani - Annoying accent and whining
Bastila - Crazy visions
Carth - Goatee styling tips

Extra Sidequests
Talk to the other members of your party often. Most have an extra side quest that can only be activated by talking to them at least 8 times during the game. Sometimes it takes even more. Bastila's, for example, has you searching for her mother on Tatooine and Carth's has you hunting for his lost son.

Finding Party Members
Bastila - Jedi Human - Taris
Canderous - Mandalorian Soldier - Taris
Carth - Human Soldier - Endar Spire
HK-47 - Combat Droid - Tatooine (buy him in the droid shop)
Jolee Bindo - Jedi Human - Kashyyyk
Juhani - Jedi Guardian - Dantooine (don't kill her!)
Mission - Tw'lek Scoundrel - Taris
Zaalbar - Wookie Scout - Taris
T3-M4 - Expert Droid - Taris

Get On Stage
Want to get on stage with the musicians in the Upper Taris Cantina? Of course you do. To manage this trick, walk against the corner of the stage and press the Black Button several times. This cycles through party members and will end up popping one of them on stage. Now sing a song for all the word!

Infinite Dark Side Points
When you arrive on Tatooine, you'll find a girl named Sasha who has stowed away on the Ebon Hawk. Keep on telling her to leave the ship as many times as you can before she actually leaves. You'll gain Dark Side Points each time you tell her to leave. If done enough times you'll reach the "Absolute Dark Side Level" (you'll know because the background has sparking fire behind your character).

Infinite Dark Side Points #2
On Manaan, when you return to the surface using the submersible, you speak to Roland Wann from the Republic Embassy. He will ask you to keep your business together a secret at which time you can tell him a bribe would ensure your silence. Saying this will earn you a dark side point. You can then talk to him repeatedly doing the same thing and earning dark side points.

Infinite Light Side Points
This is a bug that should get you infinite light side points. When you first meet Rahasia you should tell her that you are not interested in finding the son. This will get you Dark side points. Then talk to her again and apologize and then say you aren't interested again. You should get light side points for this. Repeat the apologizing, and denying as many times as needed until you have full light side points.

Bastila's Black Skivvies
Dress Bastila in a Dark Jedi robe, then remove all of her clothing/armor and she'll be in dark, sexy Sith underwear.

Big Battles
Boss fights and many big fights can be seen on the horizon. When you know you are about to have a big fight, shoot up your party members with stimulants and activate your energy shields. The time limit of the stimulants is real time during convos. So when bosses begin talking, hit A repeatedly to quickly move to the battle, so your stimulants are still active during the fight. Using stimulants will greatly improve your chances of survival.

Conserve Medpacs
A lot of times, you'll find yourself using medpacs at the beginning of the game because your ability to take a bullet isn't that great. However, don't use your Medpacs on the Endar Spire, as long as you're in that situation, you cannot die. Don't bother wasting them when you don't have to.

Dark Side Discount
After arriving on the planet Taris (and getting a Sith uniform) don't go to the lower city just yet. Instead, go to the Equipment Emporium and if the Sith body armor is equipped some items are discounted.

Economising Medpacs
When in a tough fight, using medpacs from your Action Menu take precious seconds away from your attacks, making the fight that much tougher. Instead of using your action menu, just press start, go to your inventory, then utility items, and use your medpack from there. This way you aren't getting attacked while trying to select your medpack. Or you can go to the options menu and tell the game to pause every time you access your action menu.

Heal By Leveling Up
If you're in the midst of a fight and notice an "up arrow" icon over a character's face, pause during the battle and level that character up without having to use a Medpac. (Anytime you level up all of your health is restored).

Leveling Up
Be careful when picking your Force Powers and Skills when leveling up. Once you reach level 20 (combined levels of character class and Jedi class), you can no longer level up. Make sure you have everything you want before that final level up.

Malak Boss Fight
For the final fight against Malak, after you've taken down most of his health, the Dark Lord will begin draining power from captive Jedi. You need to destroy the statis chambers with the captured Jedi inside. Use Destroy Droid if you have it. Malak boosts his power with these, so run around the entire arena destroying them (including the two on the upper tier). Then use Force Wave to knock down Malak. You must use Force Immunity or suffer some serious pain. Use Force Wave, heal, Force Wave, Heal. Continue on this pattern until he is nearly dead. Then finish off with a sabre duel.

Malak Boss Fight (Dark Side)
I'm sure some of you Dark Jedi have figured this out already but for the newbies or those in need, here's a cool trick: During the final Malak battle, beat up Malak until he explains how he kills the Jedi in Stasis tubes. You can do the same! How? If you have either Drain Life or Death Field, beat up Malak until either he runs away to heal or if you need to heal, cast a Speed power (or just run from Malak but it helps with a Speed power), target a Jedi with a RED status bar, and cast. You'll get between 48 and 230 health, depending on what attack you use. This is one benefit of being a Dark Jedi!

Quick Dark Side Points
When you leave Dantooine and head to Tatooine, you'll find a girl named Sasha who has stowed away on the Ebon Hawk. Keep on telling her to leave the ship as many times as you can before she actually leaves. You'll gain Dark Side Points each time you tell her to leave. If done enough times you'll reach the "Absolute Dark Side Level" (you'll know because the background has sparking fire behind your character)

Tach-nastics
On Kashyyk, in the Shadow Lands, if you run into a Tach, "speak" to it, and it will do a little flip. Not very helpful, but kind of cute.

Wave Your Lightsaber Around
Once you get a lightsaber (or two) press Y at any time it is equipped but disengaged to make the light sword appear. Continuing to press Y will make it look like your character is attending a rave.

Kill Good Guys on Tatooine
After helping the men defend the Sand Crawler in the desert, put on Sand People outfits (taken from dead Sand Folk) and return to the Sand Crawler. The men will attack you, thinking you are enemies. You are free to defend yourself and kill them. Truly an evil act.

Medpac Crisis
On Manaan, if you choose to poison the big fish in order to kill it, you'll also poison the water. This causes a massive shortage in medpacs for the rest of the game, driving their prices sky-high.

Perfect Fight
At any time during a battle you can pause and save the game. When in a boss battle, be sure to save at least once. This way if the tide turns and you get jacked up, you can restart the fight midway through.

Scare the Crap Out of People on Taris
When you get the Sith uniform on Taris, put it on. Don't go to the Lower City yet. Instead, walk around upper Taris and talk to people. They're all scared of you now. Go and harass the people at the Clinic for more chuckles.