I'd be tempted to go for an Xbox 360, especially if you have an HD TV. Lots of games, lots of fun, online stuff.

I'd wait until there are more longer-term games on the Wii (all you've got at the moment is Zelda, which works fine on my £30 second hand GC anyway). And PS3 is a bit expensive for something that's basically the same graphics and controls wise as the Xbox 360.

There are lots of rumours of an Xbox 360 with larger hard drive/HDMI coming out soon though, so might be worth waiting...