(un-hijacking the conversation)
Coincidentally, I was just looking for NASes myself, and just purchased one. My requirements are different from yours, so you probably won't follow my strategy, but maybe somebody else is interested.
I currently have a D-Link DNS-321 with two 1TB drives arranged in a RAID 1 array, but I've recently outgrown this. Photos really pile up quickly, using up what space I had remaining from media storage.
In the interest of not going broke, I don't want to spend money on RAID-capable hardware and extra drives. Nor do I want to spend money on all the capacity that I think I *might* eventually need, when the price of computer hardware is continually dropping.
So my strategy is to buy another NAS device, this one budget-priced, onto which I can move the real space hogs, the video files (I've got the originals on DVD for the most part, so RAID safety isn't an issue). I'll keep the photos, which are irreplaceable, on the original D-Link NAS with RAID.
I just purchased a Seagate BlackArmor NAS 110
, with 3TB of capacity, plus the eventual ability to add more via USB (although that would be slower). Total price from Amazon, $200.
(Disclaimer: The link above is to my employer's web site. I don't expect you to go buy it from there, but this gives a bit of Google Juice.)