Enclosures have many variations, too many to keep track of, and a good proportion of them being cheap models from china.
A quick google turned up the following being recommended:
Rosewill RX-358, for having a 80mm cooling fan built in.
Akasa Lokstor X31, for how easy it is to swap the drive (practically a hotswap enclosure).
Enermax Brick 3.5in, for being cheap, solid, and good data performance.
Those are for 3.5" drives, which I'm assuming is what you want for a backup solution. If you want more portability, there are 2.5" drives and enclosures too, which have the advantage of being a fraction of the size and only requiring USB BUS power (no power brick), but my experience is that they also die quicker.