What recently released games can run on my 20"inch iMac on Bootcamp?

What graphics card do you have? And I would say honestly not much, it would have to be on low to run decently I think.

Your iMac has ATI Radeon HD 2400 XT right? CoD: WaW may run at lowest settings but don't expect smooth gaming experience. You have only 1GB RAM right? Get at least 2GB but I advice you to get 4GB (it's only 50$).

If you do have an Ati Radeon 2400 XT then you could play almost anything. I have a Core 2 Duo 2.4 ghz, and the 2400 XT, and I can play Crysis. So therefore I can play any PC game.

Pretty much any new games but be aware you will have to turn the graphics settings down in many of them. Make sure you are running the most up-to-date catalyst drivers as this can make a big difference, and maybe overclock your GPU as well.