I found a forum thread at hardforum.com started by someone who was looking for a NAS suggestion. He didn't want to build a dedicated box (or reuse one) but wanted recommendations for a home NAS:
I would prefer a dedicated NAS unit over a re-purposed windows/linux box just from the standpoint of better integration of parts, smaller footprint/power requirements, and ease of maintenance so I'm wondering what the consensus is for finding something decent in the $500-$600 range with 4 bays and 10/100/1000 NIC
As suggested, look at Synology or Qnap. I had an issue with my Qnap the other day, it lost its RAID config after I powered it down, when it came up, no RAID. Even though its a 2009 model and way out of warranty, Qnap support did a remote session, ran some commands to get rid of file system corruption and I was back in business, pretty impressive
Bottom line - there was a recommendation for Drobo one for D-Link in the mix, but most were for Synology or QNAP.
- Deciding Between Synology & QNAP - Take 2 (smallnetbuilder.com)