Activate the following cheats by entering the corresponding codes:

Unlock the following bonuses depending on how you played the first The Force Unleashed:

If you have a save on your hard drive from The Force Unleashed you will unlock Training Gear.
If you complete Force Unleashed (I) with the Light Side Ending, you will unlock Ceremonial Jedi Robes.
If you complete Force Unleashed (I) with the Dark Side Ending, you will unlock Sith Stalker Armor.

Unlock the following costumes by performing the corresponding tasks:

COSTUME - HOW TO UNLOCK
Experimental Jedi Costume - Complete the game with "Light Side" Ending
Saber Guard Costume - Silver Medal in Cloning Spire Trial
The Dark Apprentice's Robes - Complete the game with "Dark Side" Ending
Tie Flightsuit - Complete "Kamino The Escape"

In the second level, go to the room with a Jabba the Hut hologram and Guybrush Threepwood statues. Destroy the three machines in the room and the Holocron for the costume will appear from the Jabba hologram.

In the first level, when you stop running away from the gunship, you will die and gain Force Points. The save point at this location makes it easy to gain unlimited Force Points. Use a rubber band on your controller to force your character continue running. After dying, your character will start running again. Allow the game to idle to gain as many Force Points as desired.

In addition to the two Holocrons that are found easily, there are an another two hidden ones. The first one is located at the big tree with two eyes with a short cave. Go near that cave and look to the right to spot the first hidden Holocron behind some branches. The second hidden Holocron can be found when you see the big rock to the left of your path. Use Force Grip to move the rock to uncover the Holocron.

ACHIEVEMENT - HOW TO UNLOCK
Padawan (50 points) - Complete the game on Easy difficulty.
Jedi Master (50 points) - Complete the game on Hard difficulty.
Jedi Knight (50 points) - Complete the game on Medium difficulty.
Jedi Grand Master (50 points) - Complete the game on Unleashed difficulty.
Amplified (10 points) - Kill 10 enemies with the lightning towers.
Kamfetti (10 points) - Kill 5 enemies with the fans on Kamino.
Imperial Painball (10 points) - Throw 10 enemies into the Kamino generators.
Droid Rage (10 points) - Control the Terror Walker and destroy all the Terror Biodroids.
Strike! (10 points) - Kill three enemies with a single 'bowling' ball.
Shattered (10 points) - Shatter 10 enemies frozen in carbonite.
Break the Bank (10 points) - Smash up 10 game machines.
Valet (10 points) - Use Vader's TIE Advanced to destroy the AT-MP.
Stay On Target… (10 points) - Get to the falling Gorog without crashing into any debris.
Master of Disaster (10 points) - Break all of the coolant tanks aboard the Salvation without dying.
Stakross Medal of Excellence (10 points) - Destroy 12 lightning pylons on the Kamino dive.
Jedi Bomb Squad (10 points) - Remove all of the Terror Spider Bombs on the Salvation.
“No match for a good blaster...” (10 points) - Kill 10 enemies using the turbolasers on the Kamino Drill Grounds.
Top of the World (10 points) - Reach the top of the Spire without falling once.
Champion (30 points) - Complete the first ten challenges with at least a Gold medal in each.
Rookie (30 points) - Complete the first ten challenges with at least a Bronze medal in each.
Challenger (10 points) - Complete one challenge and receive at least a Bronze medal.
Hat Trick (30 points) - Get a Gold medal on any 3 challenges.
Platinum (30 points) - Get a Platinum medal on any challenge.
Competitor (20 points) - Get a Silver medal on any 5 challenges.
Unleashed (10 points) - Activate Force Fury 10 times.
Enjoy The Trip See You Next Fall (10 points) - Cause 50 enemies to fall to their deaths.
Maxed Out (30 points) - Upgrade all Force Powers to Rank 3.
Use the Force, Luke (20 points) - Complete any combat level using only Force Powers.
Lucky Streak (20 points) - Defeat 300 consecutive enemies without dying.
Sky Killer (20 points) - Destroy 15 TIE Fighters.
Arachnophobia (20 points) - Destroy 200 Terror Spider Droids.
It Burns! (20 points) - Disintegrate 15 enemies by throwing them into red force fields.
Pied Piper (20 points) - Entice 10 Stormtroopers to leap to their deaths with Mind Trick.
Holocron Hunter (40 points) - Find every holocron.
Return to Sender (20 points) - Kill an AT-MP by gripping its own missiles and throwing them back.
Up, Up and Away (20 points) - Overload 20 Jumptrooper jet packs.
Passive Aggressive (20 points) - Parry and counter 10 melee attacks.
Awww Yeah… (30 points) - Perform every combat move in the game (excluding combos that require Rank 3 Saber).
To the Face! (20 points) - Reflect 20 missiles back at AT-MPs.
Specialist (10 points) - Upgrade one Power to Rank 3.
Fully Charged (10 points) - Use an entire bar of Force power on a Lightning attack. 
Escape from Kamino (20 points) - Escape Kamino in Vader's TIE Advanced.
The Nemesis in Flames (20 points) - Destroy the Gunship.
Bring Down the Giant (20 points) - Defeat the Gorog.
The Exterminator (20 points) - Defeat the Terror Walker.
Crack The Sky (20 points) - Destroy the Star Destroyer.
Meeting of the Jedi (20 points) - Reunite with Kota.
Betrayed By Rage (20 points) - Complete the game and choose the Dark Side ending.
A Measure of Mercy (20 points) - Complete the game and choose the Light Side ending.
Poor Bob (10 points) - Force Grip a Stormtrooper, impale him, zap him with Lightning, then throw him into an object.

"Battle Of Endor" achievements
ACHIEVEMENT - HOW TO UNLOCK
Returning the Favor (20 points) - Defeat a grenadier with his own grenade.
One with the Force (30 points) - Complete Endor without dying.
Sith Kicker (10 points) - Drop kick 10 Ewoks.
Holocron Hunter (30 points) - Find all the holocrons in Endor.
Victory! (30 points) - Complete Endor.
Never Tell me the Odds (40 points) - Complete Endor on UNLEASHED difficulty.
Yub Yub (25 points) - Complete the level defeating 20 Ewoks or more.
Don't Let the Wookiee win (15 points) - Defeat Han and Chewie.