At the main menu, select "Options", "Cheats", "Enter New Cheat", then enter one of the following codes to activate the corresponding cheat function. Note: Each note or chord must be strummed.

All songs in Quick Play mode -
Press Yellow + Orange, Red + Blue, Red + Orange, Green + Blue, Red + Yellow, Yellow + Orange, Red + Yellow, Red + Blue, [Green + Yellow] two times, [Yellow + Blue] two times, [Yellow + Orange] two times, Yellow + Blue, Yellow, Red, Red + Yellow, Red, Yellow, Orange to unlock all songs in Quick Play mode.
Air guitar

Press Blue + Yellow, [Green + Yellow] two times, [Red + Blue] two times, [Red + Yellow] two times, Blue + Yellow, [Green + Yellow] two times, [Red + Blue] two times, [Red + Yellow] two times, [Green + Yellow] two times, [Red + Yellow] two times.

Hyperspeed mode -
Press Orange, Blue, Orange, Yellow, Orange, Blue, Orange, Yellow. This mode makes the charts faster. There are five Hyperspeed levels. Press Green on the Hyperspeed option at the "Cheats" menu to cycle through them.

Precision mode -
Press [Green + Red] three times, [Red + Yellow] two times, [Red + Blue] two times, Yellow + Blue, Yellow + Orange, Yellow + Orange, [Green + Red] three times, [Red + Yellow] two times, [Red + Blue] two times, Yellow + Blue, [Yellow + Orange] two times.

Performance mode -
Press Red + Yellow, Red + Blue, Red + Orange, Red + Blue, Red + Yellow, Green + Blue, Red + Yellow, Red + Blue. This mode makes everything disappears except for the performance.

Through The Fire And The Flames song - Successfully complete Career mode on any difficulty setting to unlock Through The Fire And The Flames song by Dragonforce.

Bonus characters - Successfully complete the indicated task to unlock the corresponding character:

Lou: Successfully complete Career mode to unlock Lou for purchase at the store for $15,000. Lou comes with his skeleton guitar and two costumes (original devil outfit and werewolf viking).

Slash: Defeat Slash in the Boss battle in Career mode to unlock him for purchase at the store for $10,000.

Tom Morello: Defeat Tom Morello in the Boss battle in Career mode to unlock him for purchase at the store for $10,000.

Bonus basses - Successfully complete the indicated task to unlock the corresponding bass:

Beach Life: Successfully complete Co-op mode on the Hard difficulty setting.

Neversoft Skateboard: Successfully complete Co-Op mode on the Expert difficulty setting with a "Five Star" rank on all songs.

PendulAxe Bass: Successfully complete Co-op mode on the Expert difficulty setting.

Bonus guitars - Successfully complete the indicated task to unlock the corresponding guitar:

Bat: Get a "Five Star" rank on all the songs on the Easy difficulty setting in Career mode.

Distant Visitor: Successfully complete Career mode on the Expert difficulty setting.

El Jefe: Get a "Five Star" rank on all the songs on the Expert difficulty setting in Career mode.

Jolly Roger: Get a "Five Star" rank on all the songs on the Medium difficulty setting in Career mode.

Moon Shot: Successfully complete Career mode on the Easy difficulty setting.

Nemesis 13: Successfully complete Co-op Career mode on the Medium difficulty setting.

Risk Assessment: Successfully complete Career mode on the Expert difficulty setting.

Rojimbo: Successfully complete Career mode on the Hard difficulty setting.

Saint George: Successfully complete Career mode on the Medium difficulty setting.

Tiki Face: Get a "Five Star" rank on all songs on the Hard difficulty setting in Career mode.

Battle Lou in Expert mode with Easy mode notes - When the battle with Lou starts at the end of the game on Expert mode, strum without holding any frets until you lose. At the "Game Over" screen, select "Tutorial". Pick the tutorial for Guitar Battle, and play through it until the "Lesson Complete" message appears. As soon as the next fret board appears, pause the game, and exit to return to the lesson menu. Then, press Red to return to the list of songs. The battle with Lou will be highlighted. Choose the song, and Lou's notechart will now be set to Easy mode. Note: Your notechart will still be in Expert mode, but his will be in Easy mode.

Easy "Buy A Guitar Already" achievement - Successfully complete Career mode on the Hard or Expert difficulty setting. Turn the Xbox 360 off after saving your game. Plug a regular controller in, then turn your Xbox 360 on. Load the career you just completed. When you enter the character selection screen, you should get the "Buy A Guitar Already" achievement.

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

Enlightened Guitarist (30 points): Gold Star 20 songs on Expert.
Hendrix Reborn (10 points): Complete Career Lefty and Righty.
Who Needs the Power (15 points): 200k on Cult of Personality without Star Power.
Whammy Mania (15 points): Use the Whammy Bar on every held note on Number of the Beast.
Star Mania (15 points): Activate Star Power 3 times on Through the Fire and Flames on Expert.
Life of the Party (10 points): Host Ranked Online matches and win 15 consecutive songs.
Search and Destroy (10 points): Join Ranked Online matches and win 15 consecutive songs.
Too Many to Count (25 points): Hit 250,000 notes in Career.
Never Gonna Spend It All (10 points): Earn $350,000 in career lifetime earnings.
That's What Friends Are For (25 points): Complete Co-op Career.
Back Up Hero (10 points): Complete all songs as the back-up guitar player.
Guitar Wizard (10 points): Complete all Co-op as the lead guitarist.
100 Million!?! Gulp!?! (30 points): Earn 100,000,000 points total in Career.
Streaker (10 points): Earn a 150 note streak in a Ranked Online Battle mode match.
Tone Deaf (5 points): Beat any song on the expert difficulty with the games sound options turned down to zero.
Easy Rider (5 points): Complete a Career on the Easy Difficulty.
Medium Rare (10 points): Complete Career Mode on the Medium difficulty.
Always Hard (15 points): Complete Career on the Hard difficulty.
Solo Career (25 points): Complete all Career difficulties.
Button Masher (5 points): Win 15 consecutive Ranked songs online using a standard controller.
Buy a Guitar Already (15 points): Play through a career on the Hard or Expert difficulty using a standard controller.
Big 'Ol Pile of Wins (20 points): Win 500 Online Ranked matches.
The Long Road Ahead (100 points): Complete all difficulties in Career, buy everything from the shop and complete 100 online matches.
Meet Your Maker (20 points): Beat one of the creators of Guitar Hero 3 at their own game.
Right Hand of God (20 points): Complete Career Mode on the Expert difficulty.
Bronze Streaker (5 points): Earn a 100 note Streak in Career or Quick Play.
Silver Streaker (10 points): Earn a 250 note streak in Career or Quick Play.
Gold Streaker (15 points): Earn a 500 note streak in Career or Quick Play.
Streak Master (20 points): Earn a 1000 note streak in Career or Quick Play.
First Big Score (5 points): Score 250,000 on a song.
Half a Mill' (10 points): Score 500,000 on a song.
Now That's Impressive (20 points): Score 750,000 on a song.
Axe Grinder (10 points): Earn 5 stars on all songs on the Easy difficulty.
Rock Guru (20 points): Earn 5 stars on all songs on the Medium difficulty.
Shredder (30 points): Earn 5 stars on all songs on the Hard difficulty.
Guitar Hero (75 points): Earn 5 stars on all songs on the Expert difficulty.
Perfectionist (10 points): 100% a song.
Ready to Rock (5 points): Complete the tutorial.
Axe Collector (5 points): Buy all the Guitars from the shop.
Track Master (5 points): Buy all songs from the shop.
Got 'em All (5 points): Buy all characters from the shop.
A Couple of Streakers (5 points): Earn a 200 note streak in a Co-op match.
Two Timer (10 points): Earn a 500 note streak in a Co-op match.
Dynamic Duo (15 points): Earn a 1000 note streak in a Co-op match.
Streak Masters (20 points): Earn a 2000 note streak in a Co-op match.
Millionaire Club (20 points): Score 1,000,000 on any song in a Co-op match.
Higher Than Most (20 points): Score 700,000 on any song in a Co-op match.
Easy Duo (10 points): Earn 5 stars on all Co-op songs for the Easy difficulty.
Medium Duo (20 points): Earn 5 stars on all Co-op songs for the Medium difficulty.
Hard Duo (30 points): Earn 5 stars on all Co-op songs on the Hard difficulty.
Living Legends (75 points): 5 Star all Co-op songs on Expert.
Leaders of the Pack (10 points): 100% a song in a Co-op match.
Two by Four (5 points): Get an 8X multiplier in a Co-op game.
Half Mill' Club (10 points): Score 500,000 on any song in a Co-op match.
Burnin' a Hole in Your Pocket (10 points): Buy everything from the store.
The Inhuman Achievement (15 points): Complete Through the Fire and Flames on Expert.

Additionally, there are three secret achievements:

Almost Got It (5 points): Fail a song passed 90% completion.
Tail Between Your Legs (0 points): Refuse a Boss battle.
Blowin' It (5 points): Fail any song 10 times.