How big is the tank? If you have room you could have a school of smaller community fish (zebra danios, tetras, etc). Obviously no fin-nippers and I would stay away from any semi aggressive fish like gouramis. I have a five gallon with my betta and a mystery snail - they happily stay away from each other. If your tank is larger and you ultimately want to have "lots" of fish - you may consider getting your betta his own smaller tank.