I just traded in PS2 Slim, GameCube, and some games for store credit and pre-order of Zelda: Twilight Princess for the Wii at EB Games.
Definitely not all games are accepted for the "Trade 3, Get Pre-Order Free" promo.
These 5 games did NOT quality for the trade-in to get Zelda free:
X-Men Legends (GameCube)
ICO (PS2)
Wild Arms 3 (PS2)
Parappa 2 (PS2)
Resident Evil 1 (GC)
The following 3 did:
Final Fantasy X-2 (PS2)
Katamari D. (PS2)
Futurama (PS2)
Also, Futurama was pretty scratched, and no instruction booklet (don't look at me that way, I bought it used from BlockBuster), which would have counted against me for trade-in for store credit, but made no difference for the trade-in in 3, get one free promotion.
PS: I got $60 for a PS2 Slim console, and $30 for a GameCube.