Some of the best looking enclosures are those that closely replicate a snapshot of the natural habitat of the species. Put alot of thought into it, look at as many pictures of the area as you can, if possible even visit the area. Really the possibilities are endless.
In my opinion there is nothing more hideous than seeing a display enclosure with a fake rock wall, astroturf substrate, a fake hide and matching waterbowl, and the typical fake ivy housing something like a bearded dragon. Imagine the reaction of the general public if thats how many zoos designed their display enclosures. What my vision of a display enclosures is something replicating the natural habitat of a species in as much detail as possible. Something like an inland taipan on a gibber plain or similar. Another one of my pet peeves- spotted pythons being housed on red sand with the complementing sheep skull.
Some of the european hobbyists have some spectacular looking display enclosures, so looking at some photos of them may give you some ideas. Of course, it goes without saying, that the more the enclosure replicates the natural habitat, the more work involved for the keeper in the long term maintenance of such an enclosure.