Guitar Hero Classic SG
$39.99 at www.redoctane.com
This is the one that started it all, black with a white pickguard for the first game, and now palette-swapped to red with a black pickguard (the "Cherry" finish) for Guitar Hero II. It does have a cord, which is a non-plus, but it's certainly reliable.
This is the standard by which all other guitars will be judged. Styled after the real-world Gibson SG (particularly the new color scheme), with five responsive buttons, one flipper, a solid feel, bumpy start and select buttons, and an average tilt sensor inside.
Interestingly enough, Red Octane's official site appears to only sell the black and white model, but www.ddrgame.com will guarantee you the Cherry finish for $49.99 (ten bucks more).
