I was looking at the backgrounds at Petco the other day and they didn't have much of a seclection, and only one that wasn't an underwater scene -- it was black on one side, blue on the other. I'd bet, though, that if you went to a fish specialty shop you could probably find a bigger selection. I know I've seen forest scenes before. If nothing else, if the aquarium isn't too big, you could use book covers, which have a pretty wide variety of designs.