Well if you want a case that wraps the phone up, you can look at Innocases or Otterbox. If you are just after a thinner holster like the OEM one, you can look at a place like
BlackBerry 9700 Cases. They have quite a few that would seem to be the thin OEM look like you want. If you just want a good case with no real specifications go with the innocase or the commuter...