Check out which games you can get your hands on at the Nintendo Cube Clubs, and how new these versions are.
Short and sweet, because I'm about to head back to Atlanta for more! Update: Pikmin version confirmed. Also note that Eternal Darkness will not be on display during the "family friendly" hours.
Star Fox Adventures - SpaceWorld burn w/ Arwing mission and optimized graphics
Wave Race Blue Storm - Appears to be a final version, translated to English
Luigi's Mansion - Final version in English???
Super Smash Brothers Melee - SpaceWorld burn or more recent; Peach, Kirby, and the Ice Climbers are playable, and you can test out the "Adventure" mode.
Star Wars Rogue Leader - The Nintendo Show burn or more recent; mission structure is in place and it appears that you can beat missions to unlock the next one just like in the final game
Pikmin - Definitely the same demo that appeared at E3; only a training session and Days 1 and 2 are playable; the mechanics are there, but this outdated burn doesn't at all show off the game's structure or the updated graphics visible at SpaceWorld
NBA Courtside - Unsure
Madden 2002 - EA Gamers Day burn or more recent; looks drastically better than the E3 version
Eternal Darkness - SpaceWorld burn, with the new girl unlocked
Super Monkey Ball - Appears to be final version translated into English; all modes are available if you have enough Play Points (one GC demo has a memory card installed with all modes unlocked)