The security vendor sells the Imperial Dancers Outfit. The social vendor on Balmora sells the Resistance Fighter outfit. If you do a lot of space combat you can get the Pilot's outfit. Tatooine has the Sand People outfit, Dromund Kas has men's formal wear, Hoth has the Hailstorm Brotherhood outfit, ad infinitum. As far as I've seen, though, all of the unique outfits you can get that way are Light Armor. The advantage is that everyone can wear them, but the downside is that most classes will have to sacrifice their armor advantage if they can wear medium or heavy. But since all the outfit sets are modable you can keep them through most of the game. Just have to have enough social ranks, or a lot of money, or the fleet commendations.