Anything below Crysis and I believe Halo2, won't take it. I do believe Halo 2 and later does support it, but I'm not too sure. Mayber The second FEAR game will support more cores as well.
This is one of the reasons I have not bought a quad yet. Sure I've thought about it but I can't even use 100% of both my cores on my core2duo.
There are plenty of games that support 2 cores but few like crysis that support 4 cores. But whats the point of 4 core support with crysis when it doesn't use more than 60% of 2 cores.
You made the right move though. With quad core prices the way they are if I was making a new build I'd go quad too but I can't see going there on my system yet.
Quads are taking off and i'm guessing in 08 there should have many apps/games that should support 4 cores.