Depends on what types of games you like. If you like a lot of shooters, or action games then get a PS3 (or a 360 which has 90% of the same games but costs less - initially).
If you're more of a casual player then consider a 360 if Wii still isn't satisfying you.
Unlike the casual friendly PS2, the PS3 is really the most 'hardcore' system this generation.
Don't forget Wii Sports Resort with WiiMotionPlus which gives true 1:1 motion control will be out in a couple months.