My picks for betta tankmates in a ten gallon:
- pygmy cories
- ember tetras
I'd always go embers over neon tetras. Neons are larger and more active and I don't trust them not to nip. Embers are so chilled, they'll sometimes just stay still in the water for a few minutes, gossiping with the other tetras. :) They are entirely peaceful, totally non-nippy and very pretty. They develop a lovely black edge on their dorsal fin.
I have ten in my sorority and they all get on really well with my girls, even at feeding time. I think the girls are like, "What? No way something that small is even a fish!"
On the cichlid note, I do know someone who successfully housed an angelfish and a betta together (with male fancy guppies, no less) with no issues, but it was the stupidest combination I have ever seen and it should never have worked. Definitely don't try this at home, kids.