The following are Guitar Hero 2 Cheats. You want to be done with Guitar Hero 2 now that Guitar Hero 3 is coming out.

Secret Guitars

* Snaketapus Guitar: Complete Hard Mode.
* The Log" Guitar: You must achieve 5-Star every song on Expert.
* Battle Axe Guitar: Complete Expert Mode
* Casket Guitar: Complete Medium Mode.
* Eyeball Guitar: You must achieve 5-Star every song on Hard.
* Fish Guitar: Complete Easy Mode.
* USA Guitar: You must achieve 5-Star every song on Easy.
* Viking Guitar: You must achieve 5-Star every song on Medium.

Here is another set of Guitar Hero Cheats:

On the main menu, directly depress the colored key without any other input.

Performance Mode ... YELLOW, YELLOW, BLUE, YELLOW, YELLOW, ORANGE, YELLOW, YELLOW
Hyper Speed ... ORANGE, BLUE, ORANGE, YELLOW, ORANGE, BLUE, ORANGE, YELLOW
Air Guitar ... YELLOW, YELLOW, BLUE, ORANGE, YELLOW, BLUE
Eyeball Heads ... BLUE, ORANGE, YELLOW, ORANGE, YELLOW, ORANGE, BLUE
Moneky Heads ... ORANGE, BLUE, YELLOW, YELLOW, ORANGE, BLUE, YELLOW, YELLOW
Flaming head ... ORANGE, YELLOW, ORANGE, ORANGE, YELLOW, ORANGE, YELLOW, YELLOW
Horse head ... BLUE, ORANGE, ORANGE, BLUE, ORANGE, ORANGE, BLUE, ORANGE, ORANGE, BLUE
Hyper Speed ... ORANGE, BLUE, ORANGE, YELLOW, ORANGE, BLUE, ORANGE, YELLOW

And this is the last set of guitar hero 2 cheats I can find.

Unlockable Co-Op Guitars
Here is how you can unlock additional Basses in Co-Op mode

Gibson SG Bass - Beat 10 Songs

Gibson Grabber - Beat 20 Songs

Gibson Thunderbird - Beat 30 Songs

Gibson Les Paul and skin - Beat 40 Songs

Hofner Bass - Beat every song

Lava Pearl Musicman Stingray - Get 5 stars on at least 10 songs

Cream SG - Get 5 stars on 20 songs

Natural Sunburst Gibson Thunderbird Bass - Get 5 stars on every co-op mode song (stacks with below)

Natural Maple Gibson Grabber Bass - Get 4 stars on all co-op mode songs