PS3 = Shitty games with great graphics
Xbox = Great titles such as Halo 3. However you have to pay to play online.
Wii = Great games with good graphics, free internet and the Virtual Console (Lets you download old school games from NES, SNES, N64, etc. and other stuff.)
I'd get the Wii first, Xbox second and I dunno about the PS3. Maybe wait for the price to go down for that.