If your after a NAS solution, be prepared to do some research.
I really really liked the idea of the WD my world book NAS solutions, untill I read bad reviews about it being loud and slow.
Many companies now offer some form of NAS solution, but you should consider a few things.
1) final capacity you need for storage
2) connectivity, usb, firewire, ethernet, dint forget usb 3 is trying closer to becoming a new standard.
3) data redundancy, do you need raid
4) access, do you need access via the web, ssl, ssh, telnet
5) servers, do you need then for: itunes, dnla, http(s), ftp, mail etc ...
6) budget, speaks for itself.
Imho you get what you pay for. My NAS solution cost me close to