I recently acquired an HP-Proliant ML370-G4 with a PCI-X Smart Array 6404 SCSI U320 controller card that has a 192MB cache. It currently has two 146GB U320 10kRPM drives configured as a RAID0 array. I plan to add four more 146GB drives configured as a RAID5 array (it has a six disk drive cage).
The machine is built like a tank - redundant power supplies, ECC RAM throughout, hot-swap drives, six hot-swap fans, SDLT320 tape drive, etc. The quality of the hardware and thoughtfulness of the design are very impressive, especially considering that I snagged this sweet box for $200. OpenBSD is a perfect fit.