I spent about $1300 last year building a system. It was built to max out StarCraft 2 when it releases. I am a big believer on an easily upgradable casing and motherboard, everything else can come in pieces.
Last year I went with a dual card system. I have 2 fairly older cards right now. (2) Nvidia 9800 GT 512 linked, they were cheap but can play almost everything out there maxed (currently). I mainly spent the money for the case, and dual card motherboard, and my 3D monitor. The rest I just upgraded in the casing.
Some may scoff, however I went with an XPS from Dell. Mainly because the system comes with a huge, stainless steel casing. Hell, the thing weight alone screams quality casing. The casing is awesome, large enough to fit any motherboard, and fully customizable. It has a handle on the top that you just pull forward. The side pops right off exposing all components, easy for upgrade. I have had a lot of cases and this one is one of the best. (IMO) the XPS brand is awesome and in comparison to some of my other built computers, has been great. You could get an entry model fairly cheap with the case, then just go to Fry's and pick up all the additional RAM, Video Cards, ect.
