They make a clear case and all their cases for the 3G/3GS are mix and match so your choices are endless.
http://www.youtube.com/watch?v=IIlAnNyKIc0
Got the black via Amazon Prime free shipping. Also ordered a blue because I like it that much. It's a soft polycarbonate case, flexible and a great feel. Much better than those froggy cases or the other plasticky stuff.
Oh and it's far cheaper. Tight, slick and you have the option to go with only a back or the two parts, still slim fit.
Went with this for my 3GS. Had used the Casemate Signature hard leather for the 3G and 2G. Very good case but I wanted the slim case with protection. (All four corners are protected on the cozip.)
Really like it and somewhat surprised how much.