I just built this box a few months ago:

https://nerp.net/gallery/nerp

It contains (picture is of bare bones, before fully installed)

2x AMD Opteron 246 (2.0ghz)
1gb PC2700 (replacing 2x512 with 4x1024 sticks this winter)
Tyan S2882 (K8S Pro)
2x Seagate baracuda 120gb drives (software mirroring)
LZS (rackmountnet.com) Opteron 1U case (very loud, but it's a colo)

I'm currently running Debian/i386 sarge, but I am hoping that the amd64 port will have a nice stable sarge version this winter when I plan to do the ram upgrade. I had a 3ware 7500-4 (older board) and 4x 60gb Hitachi drives, but it turns out there are serious issues with 7xxx 3ware cards and the new AMD 8111 chipset (and two intel chips) that causes wierd crashes/lockups. I ended up replacing the 120gb of RAID10 with 120gb of RAID1 (linux software raid) using PATA-SATA adatpers and the onboard SATA controler. (which does crappy software raid, which I didn't use)