I'm with Denny, I build my own.
I just built one this spring when I went back to school.
1000w power supply, 8 gig of dual channel RAM (still have room for 4 more gig), AMD X64 6000+ dual core, twin Nvidia Quardro 1400 video cards. Two 500 gig SATA hard drive, 11 cooling fans-including processor and vid cards. Was thinking about water cooling until the head egghead reassured me that "they hardly leak that much more, kinda sorta". Oh yeah, a HDTV DVR card for those nights when Survivor is on and I can't get the wife to give up the remote. Also picked up a 22" LCD.
Running XP Pro, wouldn't be caught dead with that chrome polished turd called Vista.
Total $2,300
Would run over 5 thousand if I went with one of the branded manufacturers.