I guess you want a tower and not a rack-mount?
Know anything about the workload? Is it HDD-limited or RAM-limited or CPU-limited?
This looks nice: http://www.tigerdirect.com/applications ... 5&csid=_61
Only 2.13GHz CPU, though. It really depends on what you want to do, too. Probably half your costs will be on storage. Do you want RAID 5? Do the hard drives need to be hot-swap? Do you want to have redundant power supplies? How many hard drives? How much space? You can probably spec out a second quad-core CPU as well.
The benefit of something like the HP is you can offload the warranty to HP if you get that option:
HP Care Pack Services
Extended Care - HP 3 year Next business day ProLiant ML150 Hardware Support -U8184E
Committed Care - HP 3 year 4 hour 13x5 ProLiant ML150 Hardware Support - U8192E
Deployment Services - HP Install ProLiant ML150 Service - U8195E
Smart Buy Care Pack Services
HP S-Buy 4-Hour Onsite Response, 13-Hour x 5-Day Coverage, 3 years - UE897E
HP S-Buy 4-Hour Onsite Response, 24-Hour x 7-Day Coverage, 3 years - UE898E
HP SBuy3y24x7 24hCTRProliant ML150HW Sup - HZ753E
NOTE: Smart Buy Care Packs can only be attached to Smart Buy SKUs
NOTE: For more information, customer/resellers can contact: http://www.hp.com/services/carepack
One trick with the hard drives is you can try calling or contacting CDW and seeing if they have any backstock hard drives available--especially for HPs, they often have a bunch for pretty good prices. Customers configure stuff and then decide to not get it and the drives are already used and tested, just put back into the warehouse. You might also get some decent prices on eBay.
If you dink around with HP server stuff at all, I recommend http://h18006.www1.hp.com/products/quic ... l#CD_Files
which is handy for looking up certain models, finding some SKUs to look up elsewhere like at http://partsurfer.hp.com/Search.aspx