At the main menu, select "Options", "Cheats", "Enter New Cheat", then enter one of the following codes to unlock the corresponding cheat option:

Performance Mode - Press Yellow(2), Blue, Red, Blue, Green, Red(2).

Hyperspeed - Press Green, Blue, Red, Yellow(2), Red, Green(2).

Auto Kick - Press Yellow, Green, Red, Blue(4), Red. The bass drum pedal will now be played automatically. Note: Enabling this code will disable earning any money after a song has been completed.

Unlock Quickplay - Press Blue, Blue, Red, Green(2), Blue(2), Yellow.
Aaron - Press Blue, Red, Yellow(5), Green.
Nick - Press Green, Red, Blue, Green, Red, Blue, Blue, Green.
Johnny Viper - Press Blue, Red, Blue(2), Yellow(3), Green.
Rina - Press Blue, Red, Green, Green, Yellow(3), Green.
Air Instruments - Press Red(2), Blue, Yellow, Green(3), Yellow.
Invisible Characters - Press Green, Red, Yellow(3), Blue(2), Green.
AT&T Ballpark - Press Yellow, Green, Red(2), Green, Blue, Red, Yellow.
Gem Color - Press Blue, Red(2), Green, Red, Green, Red, Yellow.
Flame Color - Press Green, Red, Green, Blue, Red(2), Yellow, Blue.
Star Color - Press Red(2), Yellow, Red, Blue, Red(2), Blue.
Vocal Fireball - Press Red, Green(2), Yellow, Blue, Green, Yellow, Green.
Always Slide - Press Green(2), Red(2), Yellow, Red, Yellow, Blue.
Extra Line 6 Tones - Press Green, Red, Yellow, Blue, Red, Yellow, Blue, Green.

"Pull Me Under" song - Successfully complete an entire career with any instrument. "Pull Me Under" can be played during the credits. Once done, it will be unlocked.

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

Billy Corgan: Play "Today" in Band Career mode.
Hayley Williams: Play "Misery Business" in Vocals Career mode.
Ozzy Osbourne: Sing "Mr. Crowley" and the encore song at the "Germany: Ozzfest" gig in Vocals Career mode.
Rockubot: Successfully complete Drum Career mode.
Skeleton: Successfully complete Vocals Career mode.
Sting: Play "Demolition Man" in Bass Career mode.
Ted Nugent: Win Ted Nugent's Guitar Battle in Guitar Career mode.
Travis Barker: Play "Dammit" in Drum Career mode.
Zakk Wylde: Win Zakk Wylde's Guitar Battle, and play the encore song with him at the "Louisiana: Swamp Shack" gig in Guitar Career mode.

Easy vocals - To score 100% on vocals, turn up the volume so the microphone can pick up the in-game singing. You should get 100% in any song.

Chuck Schuldiner (Death) custom character - Use the following customizations:

Head

Nose: Narrow
Mouth: Smallest
Eyes: Little smaller and deeper; Color: Brown
Facial Fair: None

Body

Skin: Tan
Proportions: The tall buff in shoulders one
Presence: Calmer ones
Hair: Curley Cue; Color: 2nd Darkest Brown

Outfit

Torso: Very Casual; Color: Black
Pants: Deez Denims; Default
Shoes: Axel Kickers; Default

Instrument

B.C. Rich Stealth
Style: Manta
Finishes: Custom Color Black
Fret Board: Ebony
Inlays: Dots
Head Stock: Shredder
Finishes: Custom Color: Black
Pickguard: None
Pickups: Supersonic 2 Color Black
Knobs: None
Bridge: No Whammy
Strings: Default

Dimebag Darell custom character - Use the following customizations:

Head

Face: For the scaling, make his face and jaw bigger, and give him brown eyes.
Facial Hair: Fine Goatee

Body

Skin Tone: Tan
Proportions: The one close to the end, making him heavy in middle
Tattoos: Anything that looks good on left or right arm
Presence: Anything wild or really calm
Hair: Curley Cue; Color: Darkest Orange

Outfit

Torso: No Sleeves Please; Color: Black
Pants: Camo Whamo!; Color: Default
Shoes: These Oh Things?; Color: Default
Accessories: Left Arm: Banded Bracer; Color: Black, Right Arm: Little Banded Bracer; Color: Black

Instrument

Cowboys From Hell Dean ML Guitar
Body: Dearth Fader
Finishes: The Forge
Details: None
Band Logo: None
Fret Board: Ebony
Inlays: Dots silver
Headstock: Veejay
Finish: Solid Black
Details: Truss Cover
Pickguard: None
Pickups: Supersonic Black
Knobs: Bellenders: Black
Bridges: Whammy Bar:Black
Strings: Your choice

Note: If you do not like the "cowboy from hell" look, change the body finish to: Boltz, Bookmatch color orange, Detail: Pinstripe: Black, Firestarter.

Kurt Cobain (Nirvana) custom character - Use the following customizations:

Head

Nose: Narrow larger at tip
Mouth: Top: Smallest; Bottom: Third smallest
Eyes: Little larger and deeper; Color: Hazel
Facial Fair: 5 o Clock Shadow; Black

Body

Skin: Pale
Proportions: Skinny and tall one
Presence: Calmer ones
Hair: Seattle's Finest; Color: Second lightest brown

Outfit

Torso: Layered T: Color; Default
Pants: Deez Denims; Default
Shoes: Slips Ons; Black

Instrument

Fender Mustang
Style: Treble Maker
Finishes: Custom Color: Second darkest blue row, then second darkest within
Fret Board: Ebony
Inlays: Dots
Head Stock: Style: T-bone; Color: Same as body
Pickguard: Style 1; Color: Third, gray but it looks white
Pickups: Strates Three: Black
Knobs: Speedsters
Bridge: Defender; same color as pick guard
Strings: Default

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

Learning the Ropes (5 points): Complete a tutorial.
One Time Solo Artist (5 points): Completed a song (Solo).
Stix (5 points): Perform as a Drummer (Band or Solo).
Yodeler (5 points): Perform as a Vocalist (Band or Solo).
Pick and Axe (5 points): Perform as a Guitarist (Band or Solo).
Feeding the Beast (5 points): Upload a song to GHTunes.
Download Junkie (5 points): Download a few songs from GHTunes.
A Pair Beats A Pair (5 points): Complete an Xbox LIVE 2 v 2 Pro Face-Off match (win or lose).
Survival of the Fittest (5 points): Complete an Xbox LIVE Battle Mode match (win or lose).
Mine is Bigger Than Yours (5 points): Complete an Xbox LIVE Band v Band match (win or lose).
First of Many (10 points): Complete a gig (Band or Solo).
One Man Band (10 points): Perform as every instrument at least once (Vocals, Lead, Bass & Drums).
Should We Stick Together? (10 points): Complete a song in a band (4 player band) .
50 Note Posse (15 points): All band members get a 50 note streak at the same time (4 player band).
Easy There (25 points): Complete a Career on easy (Band or Solo).
Solo Artist (25 points): Complete a solo career (any difficulty).
Band on a Mission (25 points): Complete the majority of the gigs (Band or Solo).
Bling, Bling (30 points): Earn $1,000,000 in lifetime earnings.
Top of the Charts (30 points): Complete a band career (any difficulty).
Medium Musician (30 points): Complete a Career on medium (Band or Solo).
Solid Gold Rockstars (30 points): 100% a song as a band (4 player band).
Platinum Rockstars (50 points): 100% a song as a band, hard or expert only (4 player band).
Hardcore (60 points): Complete a Career on hard (Band or Solo).
Hall of Famer (100 points): Complete a Career on expert (Band or Solo).
Jack of All Trades (150 points): Complete all instrument careers - any difficulty (Band or Solo).

Additionally, there are 25 secret achievements:

Stamp Of Approval (5 points): You created your own band logo.
One Of A Kind Axe (5 points): You created your own custom guitar.
Warrior Of Rock (5 points): You created a male band member.
Custom Beats (5 points): You created your own custom drums.
Rock Maiden (5 points): You created a female band member.
Inked (5 points): You created a custom tattoo.
Leading Lady (10 points): You rocked out as Hayley Williams.
The Experience (10 points): You rocked out as Jimi Hendrix.
The Dark Prince (10 points): You rocked out as Ozzy Osbourne.
Pumpkin Smasher (10 points): You rocked out as Billy Corgan.
Bad to the Bone (10 points): You rocked out as the Skeleton.
Wylde Man (10 points): You rocked out as Zack Wylde.
Motorcity Madman (10 points): You rocked out as Ted Nugent.
Don't Blink (10 points): You rocked out as Travis Barker.
Shiny Metal Thingy (10 points): You rocked out as the Rockubot.
Guitarist's Coattails (10 points): Get the highest score in the band as the lead or bass guitar (4 player band).
Vocalist's Coattails (10 points): You got the highest score in a band as the vocalist.
1.21 Jigowatts?!?! (15 points): All band members activated star power at the same time.
Super Group Unite (15 points): You earned an 8x multiplier with the rest of the band at the same time.
Axe Museum (20 points): You unlocked all of the guitars.
Get Your Boogie On (30 points): You scored 222,222 or higher on the song Satch Boogie as the Lead guitarist.
Muse to my Ears (30 points): You scored 222,222 or higher on the song Assassin as a Drummer.
Mike Checka' (30 points): You scored 123,450 or higher on the song Beat It as a Vocalist.
Heavy Metall... (35 points): You scored 444,444 or more on the song Trapped Under Ice.
TOOL of Destruction (35 points): You scored 444,444 or more on the song Schism.