I like TigerDirect. They have a warehouse outlet about 30 minutes from my house, so I save on shipping.
The GioCade cabinet was upgraded with a 1.4 ghz duron machine that cost about $80.00. It has a Soyo motherboard and case. So far it works great. GameLauncher appears to have a problem with the video driver and locks up when you exit a game, but MAME, Daphne and Visual Pinabll all work great on it. I'll be putting Kymaera on that machine the next time I get to the guy's house.
My cabinet has a 1.6 ghz Duron Mercury motherboard in it. That deal came to $180.00 after rebates and include CD-RW, 40gig HD, ATI Radeon 7200, memory, case, power supply, mouse, and keyboard.
I also bought a D-Link DI-604 broadband router there for $20.00.