Unlock All Code (North American Version)
The unlock all code will unlock Izzy Sparks and the Grim Reaper, along with all the bonus songs and guitars in the game. Press the right fret button sequence on the main menu. The code is "yellow, orange, blue, blue, orange, yellow, yellow." A short sound will play to indicate if the code is correctly entered. You only need to press the fret button while entering the code; you do not need to strum. This code will disable the ability to save, so you cannot save anything unlocked in this manner for later use.
Unlock All Code (European Version)
The European version of the game has an unlock all code that gives the same benefits as the North American version, but the code is different. The unlock all code is "yellow, orange, orange, yellow, blue, blue, yellow." This code will also prevent you from saving the game.
Unlock Glitch
Each difficulty level has a separate unlock store and money. This means unlocking Izzy Sparks or the Grim Reaper only allows you to use him in one difficulty level only. A glitch in "Guitar Hero" allows you to get around this in career mode. You must have the characters unlocked in one difficulty level. Select the character in that difficulty level and save the game. Go to a different difficulty level you have never played before. On the character select screen, press the Green fret button. You will automatically use Izzy Sparks or the Grim Reaper even though he is not unlocked. You will be able to save this progress.
Easiest Permanent Method
The easiest way to unlock both Izzy Sparks and the Grim Reaper without disabling saving requires starting a new band. Go immediately to the easy difficulty level. Play through the songs until you have earned $13,000. Buy Izzy Sparks and the Grim Reaper. Set one as your character. When you enter another difficulty level, you can use either character because of the unlock glitch, and you will still be able to save the game.