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

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)

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.

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

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.

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.

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.