I just added a two or so inch gravel bed, with a nice looking tiki statue in the middle of the tank. A cool and unique feature you can add to your tank is some aeration through an ornament or statue. For example, I took the airline tubing and drilled two small holes in the tiki's nose, as if it were nostrils. It came out great and adds great oxygen exchange to the water, besides the cool cosmetic look it provides. Also, I would recommend you get a plant or two, if you have a light on your tank, because when the guppies breed, they will eat their newborn fry. This will provide a "safe haven" in order to increase their chances of survival.