I'd get a 360...gears of war 2, banjo kazooie nuts and bolts, L4D (if you don't have a pc), fable 2...then you have forza 3, crackdown 2 & more to look forward to. Plus there are some nice RPGs on the 360 that you could check out...like LO and the new star ocean one.
360 arcade is pretty cheap as well, and will suffice if you can go without online or if you have a gaming pc that you can play online with...
Given that you're selling your ps3...you'd also have to factor in that the only way you will be able to play games like bioshock 2, AC2, or call of duty MW2 is if you have a gaming pc, or you get a 360.
Personally I would not go for the wii unless you really have cash to burn. I think you will get more use and more value from a 360 (arcade).
P.S. I don't know much about the games on the 360 (not as a 360 fanboy anyway) so best to do some more research into the games it has.
