The white cloud mountain minnows would be better than neon tetras. The neons have occasionally been known to nip at long fins (definitely a bad thing) and they aren't quite as zippy as the minnows, who will be able to outswim your betta if he gets mean.
There are a few varieties of the white clouds. There's the standard white clouds, long fin white clouds, and (my favorite) golden white clouds. All of these would do best in a group of at least five because they like to school together like the neons.