Platies are good, so are mollies, swordtails, and endlers. If you want a fish that is sorta hard to breed but brings in some better money I'd go with german blue rams. I've heard their easy to breed if you get a pair, but I may be wrong. If you do go with the livebearer group I'd go with endlers because they won't eat their young and are usually harder to find. Plus they look cooler!