Gold Instruments
Description: unlock a golden form of any of the four instruments (guitar, bass, drums, and mic),

How to: Beat Solo Mode on any difficulty you choose. You must also use the instrument you intend on unlocking in beating Solo Mode, so that if, for example , you wanted to unlock the Golden Drums, you should use the Drums in Solo Mode.

Silver Instruments
Description: unlock a silver form of any of the four instruments (guitar, bass, drums, and mic),

How to: Beat Bonus Tour Mode on any difficulty you choose. You must also use the instrument you intend on unlocking in beating Bonus Tour Mode, so that if, for example, you wanted to unlock the Silver Drums, you should use the drums in Bonus Tour Mode.

Transparent Instruments
Description: Unlock the "transparent" series of instruments (which gives you a transparent bass, guitar, drum kit and microphone)
How to unlock: Enter the Hall of Fame on that instrument. So, if you want the transparent bass, enter the Hall of Fame as a bassist.

Gold Fender Stratocaster
How to unlock: Complete Solo Tour mode with the guitar.

Silver Fender Stratocaster
How to unlock: Complete the Bonus Tour option on Solo Tour with the guitar.

All Songs
Wwant to unlock every song in the game (which disables the ability to save)?
How to unlock: Go to the game's title screen and insert the following code on any instrument:
Red, Yellow, Blue, Red, Red, Blue, Blue, Red, Yellow, Blue

Gold Microphone
How to unlock: You need to score a million points or more in Solo Tour.