Do you want a four-bay NAS without spending an arm and a leg? Do you need to be able to access it through the internet? Are you looking for some features such as DLNA but don't need the extensive (and expensive) array of features from QNAP and Synology? Then the D-Link DNS-345 ShareCenter Quattro is not a bad choice. The performance of this NAS device isn't bad either.
It has a sturdy case, and is equipped with a display with a number of features. You do have to accept some peculiarities of this brand, such as how to configure the network ports and sharing folders. You can buy it for as little as £199, which makes this a decent buy.