In my fw planted tank I keep discus, angelfish, neon tetras, corydoras catfish, and otocinclus without any issues. That tank is a South American type tank with tons of plants and driftwood. I keep the water very warm and very soft and acidic. I'd recommend the same for keeping neons. I will mention that neon tetras don't have an incredibly long life-span. I find myself buying two dozen about once a year to keep the numbers up. You could also keep live bearers such as mollies and swordtails, which both come in a lot of colors. Another nice option would be looking into killifish. They are somewhat difficult to find, but are very attractive fish available in many colors, although some of the larger varieties MIGHT eat neons. That's all that comes to mind right now, but if I think of more I'll post them.