Below is the current config that I have set up for all the testing/installing, etc. that I do as part of this blog.
2x Dell 1950 2x Xeon 5130 @ 2.00GHz w/ 8GB RAM and 4x 73GB 10K 2.5" SAS HDD in RAID 5
runs: VMware ESXi 4.1 build-260247
2x Dell 2850 2x Xeon DC @ 2.80GHz w/ 8GB RAM and 6x 146GB 10K 3.5" SCSI HDD in RAID 5
runs: OpenFiler 2.3 x86_64
Connecting the two is a Linksys SGE2000 running Jumbo Frames for
1GbE connections, and I'm serving up the storage from the 2850 as iSCSI
storage to the 1950.
Finally, I have an APC SMX1500RM2U SmartUPS protecting everything from power bumps (I would get some occasionally that weren't enough to power off the systems, but were enough to make them reboot). It provides about 5-7 mins of run-time currently.
Everything runs off a single 15A 120V circuit in my basement. Total cost: ~$2600 - $3000. This assumes you already have cooling for your room.