build one yourself... it's not hard.
first step: buy a case
Here is a site that I've bought some stuff from, and they where very good.
Second step: decide what you want in it... a bunch of people are crazy for newegg.com, but I have never personally dealt with them. the things you'll need are a motherboard, processor, video card, RAM, cd/dvd rom(s, / burners), hard drive(s), and possibly a bigger power supply.
My current setup (which is a very decent setup) in an intel p4 3.2gig (with hyperthreading) processor, 2 gigs of ram. A visiontek video card based on the ATI x1300 hardware (512mb instead of 256mb), one 40 gig hard drive for main programs, and a 200 gig hard drive for games and shows. One dvd burner, one cdburner/dvd rom, a floppy (yes, I am ghetto like that

), a 750W power supply, and a buttload of lights and fans. Basically looks like
this except I have a second hard drive cooler under the one on top, and I have a better processor fan now (I'll be upgrading to water cooling as soon as I get my entertainment center built though.