No to neon tetras and harlequin rasboras. They both school and are too active. (If your Neons just sat around, Kevin, then there was something wrong.)
Also, typically it's suggested you get a filter rated for two times the size of your tank even when you're not overstocking.
Your options are limited: 1 african dwarf frog, 1 betta, snails, shrimp. There's not much readily available for that size tank.
Edit: i should clarify, by readily available i mean typically found in stores.