Edgestore do a series of USB / eSATA DAS units.
2, 4, 5, 8 bays respectively.
My friend has the 801T;
It's a little picky with drives.
The RAID will only work up to 5 drives (out of 8).
Apart from that, he hasn't had any problems with it.
I suppose, if you need that feature! He uses it with WHS and drive extender handles all 8 drives without a problem
It comes with an 2 port esata PCI-E card just incase you don't have them...
Most units like this are NAS these days, but I'm sure you could find more DAS ones if you hunt around.