Just so you guys know... Doom 3 will Not come out for PS2 OR Xbox. If it does, it will suck horrendously. Doom 3's minimum requirements (for smooth play) for PC will be like a Radeon 9700, 2GHz, 512mb DDR... that hardware literally blows away PS2 and XBOX hardware. They will have to dumb it down sooo much that it will suck (just like Halo).
I have a Gamecube because I am also a PC gamer and if I wanna play Shooters, GTA type games, or Online games, I will play it ONLINE on my PC. I have a Gamecube because it is great for cartoonish type FUN games.
Ok... Now that we have that outta the way:
I recommend Tony Hawk Underground and Mario Party 5.