Oh heck that's easy, just pick any random DIY enclosure* and add your own drive... Most DIY enclosures don't put the HDDs to sleep properly, and as an added upside you'll have a full warranty on the drive (3-5 years depending on what you put into it), whereas many of the pre-fab externals from Seagate & WD often short-change you on the warranty period.
You'll have a full warranty on the enclosure too FWIW (my current Ultra enclosures come w/a 3 year warranty I think). I've had two external enclosures die in about 6 years, and in either case the drive that was inside survived intact. First one was a WD pre-fab (out of warranty, what a pain it was to yank 250GB the drive out, still using it on a TiVO), 2nd one was an ABS Venus that had a 500GB Seagate inside, still using it just fine.
*Preferably an enclosure w/active cooling or full metal housing and a drive retention system that touches the sides of the drive since most of the heat is dissipated around the sides. You could opt for one w/eSATA too to optimize backup speeds (if Win 08 Server plays nice w/eSATA, I'm pretty ignorant on that subject). Edit: The 3.5" Ultra enclosure in my sig seems to dissipate heat pretty well, tho it wasn't all that cheap ($40-ish I think).
Ironically the 2.5" version was only $25, and it also has eSATA+USB. You'd think having to cram the same bridge chip into a smaller package would make it more expensive... I guess all the extra aluminum might actually be more expensive than anything else.