Any of the live bearers are ok with each other. platys and swordtails come in lovely colours and the ratio is best as one male and 2 or 3 female. A couple of corydorus catfish will eat all the food dropped to the bottom of the tank and so keep it clean. zebra danios and leopard danios are also an interesting fish to watch, you will need a small shoal of these, say a dozen or so to start with. Most fish suppliers usually sell multiples at a discounted price, like 12 for �10.