SilverDollars are ideal. I keep 6 with an Oscar and they are too fast for it. He also has a common pleco (P.Disjunctivus) for tankmates. Also you can try Bala Shark, Clown Loach, Croaking Gourami, Firemouth Cichlid, Jack Dempsey, Pleco (Common), Sunshine Pleco L014, Texas Cichlid, Tinfoil Barb. Ive had bala sharks in with it and there is no fighting because the Bala is fast and high-strung (However, they should be kept in groups of 6).
No matter how you set it up, you're going to need a good sized tank as the ones I listed are not small fish. You can also forget about decorating the tank. Decor or plants will be destroyed.