I like drobo or the OWA (outer world computing) brands. Drobo has a hybrid-raidless technology that in theory is better than RAID where it can typically falter.
My experience of RAID is unless its enterprise grade RAID drives/ Controller you don't want it. Too many false rebuild failures etc... I ended up returning all RAID NAS i bought.
If you go the NAS route, expect slow performance unless you opt to use the ISCSI protocol. Drobo Pro allows ISCSI but you will spend an arm and a leg for it. (worth it in the end)