PC upgrade suggestions

I am starting to think about upgrading my PC (desktop) to play the newer games. I need to stay under $800 (the cheaper, the better). I know some of you out there know a lot about what's good out there. I would only need the tower. I especially like first person shooters and MMO's.

Thanks

Doug

Are you upgrading a current pc you have or looking to upgrade to a whole new PC?

I'll probably get a new desktop, but I only need the desktop without a keyboard or monitor.

It looks good, but I'd have to find someone to assemble it. There is no way I'd try and do it myself.