I'm actually half way through quoting 20 machines for a similar purpose, the specs I'm doing is:
2x Opteron 242
Tyan K8W motherboard
4x 512mb ddr ecc reg
Asus FX5200 Dual DVI
Seagate 80gb 7200rpm (boot)
2x Seagate 80gb 7200rpm SATA (data)
other worthless shit
2x 19" LCD's with DVI
Their purpose isn't rendering, it just requires pure cpu power. I've given them the option to go to 244 or 246 cpu's, as well as up to 4gb or ram, or an array of 4x raptors in raid 10 for data.
myself, I just can't wait to build the things 
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2x P3 1100's at 1400, Abit VP6, 2x Corsair 256mb PC150 sticks, 20gb 'cuda ATA-III, 2x 40gb 'cuda ATA-IV in raid 0. 20" Trinitron. No fans
2x 2400+ at 2288mhz (16.0 x 143), Iwill MPX2, 2x Kingmax PC-3200 256mb sticks, 4x 20gb 60gxp in Raid 5 on a Promise SX6000. Asus Ti4200 320/630. Cooled by Water
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