At the main menu, choose the "Options" selection, then select the "Enter Code" option. Then, enter one of the following codes to activate the corresponding cheat function:

Play as General Rahm Kota - Enter "MANDALORE" as a code to unlock General Rahm Kota.
Kento's Robe - Enter "WOOKIEE" as a code to unlock Kento's Robe.
Sith Robes - Enter "HOLOCRON" as a code to unlock the Sith Robes.
Ceremonial Jedi Robes - Enter "DANTOOINE" as a code to unlock the Ceremonial Jedi Robes.
Sith Stalker Armor - Enter "KORRIBAN" as a code to unlock the Sith Stalker Armor.
New combo - Enter "MARAJADE" as a code.
Amplified damage - Enter "LIGHTSABER" as a code.
Max force powers - Enter "KATARN" as a code.

Clone trooper helmet in TIE Fighter factory - When you reach the point in the factory where the TIE Fighters attack you, there are metal beams you can bend. Bend the last one backward, and make it a sort of step. Jump on the bent part, then jump again. Look at the roof of the hallway and jump there. There is a clone trooper helmet on the ground.

Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Apprentice (75 points): Complete Game - Apprentice difficulty. Do not change the difficulty after the game has started.
Sith Warrior (100 points): Complete Game - Sith Warrior difficulty. Do not change the difficulty after the game has started.
Sith Lord (100 points): Complete Game - Sith Lord difficulty. Do not change the difficulty after the game has started.
Sith Master (100 points): Complete Game - Sith Master difficulty. Do not change the difficulty after the game has started.
Pushed (5 points): Defeat 100 enemies with Force Push.
Gripped (5 points): Defeat 100 enemies with Force Grip.
Shocked (5 points): Defeat 100 enemies with Force Lightning.
Repulsed (5 points): Defeat 100 enemies with Force Repulse.
Impaled (5 points): Defeat 100 enemies with Saber Throw.
Stormed (5 points): Defeat 100 enemies with Lightning Shield.
Grappled (15 points): Defeat 100 enemies with a grapple move.
Launched (20 points): Defeat 100 enemies with Aerial Ambush juggle combos.
PROXY Won't Be Happy (15 points): Destroy 35 droids.
Rebel Leader (15 points): Defeat 500 Imperials.
Bossk (15 points): Defeat 200 Wookiees on Kashyyyk Prologue.
Bully (15 points): Defeat 25 Ugnaughts or Jawas.
Skilled (5 points): Earn 250,000 Force Points on a single level.
Expert (10 points): Earn 500,000 Force Points on a single level.
Legend (25 points): Earn 600,000 Force Points on a single level.
Frenzy (5 points): Get a Frenzy x4 bonus.
Sith Frenzy (10 points): Get a Frenzy x8 bonus.
Sith Lord Frenzy (15 points): Get a Frenzy x12 bonus.
Holocron Collector (75 points): Collect all Jedi holocrons in the game.
Corellian Star (10 points): Complete all bonus objectives on one level.
Force Push Mastery (20 points): Defeat 500 enemies with Force Push.
Force Grip Mastery (20 points): Defeat 500 enemies with Force Grip.
Force Lightning Mastery (20 points): Defeat 500 enemies with Force Lightning.
Force Repulse Mastery (20 points): Defeat 500 enemies with Repulse.
Lightsaber Throw Mastery (20 points): Defeat 500 enemies with Saber Throw.
Lightning Shield Mastery (20 points): Defeat 500 enemies with Lightning Shield.
The Bigger They Are (15 points): Defeat 6 Rancors.
The Harder They Fall (15 points): Defeat 10 AT-STs or AT-KTs.
Cannon Fodder (15 points): Defeat 150 Stormtroopers.
Sith Trials (20 points): Complete all Training Room challenges and Combat Modules.
Sith Training (20 points): Complete all Training Room lessons.

Additionally, there are twelve secret achievements, one of which is currently unknown:

Invasion (10 points): Complete Level - Prologue.
Insurrection (10 points): Complete Level - TIE Factory, act 1.
Junkyard (10 points): Complete Level - Raxus Prime, act 1.
Jedi Hunt (10 points): Complete Level - Felucia, act 1.
Empirical (10 points): Complete Level - Empirical, act 2.
Vapor Room (10 points): Complete Level - Cloud City, act 2.
Skyhook (10 points): Complete Level - Kashyyyk, act 2.
Infestation (10 points): Complete Level - Felucia, act 2.
Destroyer (10 points): Complete Level - Raxus Prime, act 2.
Redemption (20 points): Complete Game - Light Side.
Secret achievement (20 points): Unknown.
Worst Day-Shift Manager Ever (10 points): Kill 12 Stormtroopers as Vader during the Prologue.