If you buy a premade box, Seagate's Free Agent has a model or three that does both USB and eSATA. Or, you could make your own: get a Seagate drive of the size / budget you want and an enclosure that fits your needs. Apricorn enclosures are very popular here:
http://www.newegg.com/Product/Produc...&name=APRICORN.
Just make sure to get a drive that fits the box.