I've got a lite-on eTAU108 that does that. Its special party trick, besides running of usb, is that it can write proper booktype DVD-ROM which not many can do ;-) Well worth it in order to backup your cars SatNav disc for example.
I hadn't realised that the external superdrive couldn't be used with any Mac I bought one to use with my Air on the basis that it would also be used with my Mini that only has a combo drive. I haven't opened it yet so may return it.
Any recommendations for an external bluray drive ?