The Netgear ReadyNAS units have been getting some very good reviews in recent months. I friend has the 4 drive version and has been very happy with that running a RAID 5 setup. No problems to date with it either.

In long testing reviews/features I've read, whilst te QNAP NAS's have received good initial reviews, they can start to cause issues when a drive develops some bad sectors, and can lock up the client PCs access the NAS. In contrast the Netgear ReadyNAS has continued to handle faulty HDDs very well and handled the data by continuing to serve it from the other good drives until the faulty one was replaced. I would therefore recommend the Netgear based on what I've read so far.

There was a recent review of a couple of new business NAS units that were very good. I will dig those out and post what they were for you in the morning in case they were also something worth looking at.