How big a NAS do you want? They have at least 6tb now! Too bad they're too large for most computers to directly connect, as the 2tb/3tb/4tb barriers can be pesky.
I was looking at this recently myself. For now, I still choose to run a computer 24/7 on a battery backup to serve files across the house, to all our devices. It's basically our home server, and it has about 20tb of drives, with about 40tb more to switch out as needed (my whole DVD collection backed up as ISO).
If I were to do it, I'd probably go for WD myself. Maybe that's a bad choice, as I've not researched it in depth, but my cursory research showed that they had great reviews. True, there is other hardware out there, but I don't know that it's needed. Most are for advanced features (interchanging drives, etc) that we'd not need at home (non-upgradable unit).
http://www.amazon.com/gp/product/B00...RRCVAGC6GKQRHS