I'm pretty sure most 'sharks' will eat the neons and possibly the guppies. Also, ottos do better in groups of at least 3-5. You could maybe try twig catfish... Angelfish might be nice too!
My adventures in keeping Indostomus crocodilus, the crocodile toothpick fish. AKA armored stickleback, paradox fish, and freshwater pipefish. Care is (to the best of my knowledge) exactly the same as Indostomus paradoxus.
I see that you don't have the tank fully covered, so my idea of Roseline barbs is gone. They really do look nice though, especially in a group of about 6 or more. You could also go with some Congo tetras (at least 4). To me, a true community tank has at least 2 Angelfish, but that is up to you.
Mage - The other hobby
No planted tanks currently running (11/26/2014)
Denisan barbs, or rosealine sharks, would look great there really peacefull i have 4 in my 55 gal planted community tank, there so timid that even the 5 black neon tertas i have in the tank school with them, or you could do dwarf cichlids like rams and cockatoo cichlids, i also have them in the tank with the denisan barbs they look realy nice