I maintaind the ssd database that is listed in the sticky at the very top of this ssd forum section. I do have some external USB solid state drives listed and there are a couple of tecyhnical reviews. Here is the link:
Scroll down to the brands you are interested in and follow the links to the technical reviews. I just took a quick look there are a few other external USB ssd's available from other companies. You'll have to look in the interface column and/or the comments column to identify the external USB ssd's.