Systems I would NOT own: XBox and XBox 360
PC, why? it ends out being cheap because it is a all in one deal; gaming, school, work, social networks, chatting, everything all in one, plus i have Console controllers in general.
I have recently added a Wii and a PS3 into my arsenal (got lucky with a promotion at Best Buy on that one).
I'll be picking up COD4 or UT3 soon, and Motorstorm came with my system, so those are all my online capable games other that Madden 2007 (which you can pick up for $10 almost anywhere now I think).