I ended up getting a mini storage tower from Addonics:http://www.addonics.com/products/raid_system/mst4.asp
I chose the mini storage tower as it has a smaller footprint. The mini storage tower doesn't support removable bays for 3.5" drives (although it would for 2.5" drives), but I don't have a need for that functionality.
The model I chose has a single eSATA port on the back, and comes with a hardware port multiplier. (I don't really need a HPM, as the software PM would do, but it wasn't that much extra).
I connect the box to my laptop using the 2-port expresscard adapter:http://www.addonics.com/products/host_controller/adexc34-2e.asp
My laptop has an expresscard slot so this is very convenient -- and very fast.
The storage tower supports SATA drives, so right now I'm using a pair of Western Digital Cavier 500GB SATA drives (WD5000KSRTL):http://www.amazon.com/gp/product/B000FBSREK/sr=8-13/qid=1196806424/ref=dp_cp_ob_title_1?ie=UTF8&qid=1196806424&sr=8-13
I'm starting to accumulate 2.5" drives (as I expand the capacity of the internal drive of my laptop), so I'll probably pick up a mobile rack so I can mount the drives in the tower:http://www.addonics.com/products/Saturn/aesmr.asp