Panda cories are a no go, although they're a smaller cory (which is good for a smaller tank), they prefer cooler temps than what a betta should be kept in.
I'm really not familiar with neons or tetras.. I'm sure someone will come along who is, but whenever putting more fish in w/ a betta, you're going to have to watch the tank like a hawk.
Making sure that the betta isn't being too aggressive, and also making sure that the other fish aren't making the bettas long fins a target.
So if you decide to try out more fish w/ the betta, first, make sure the fish are appropiate for a 10gal tank and the tank conditions match up w/ the other fish and make sure you have a backup tank if you have to seperate the fish if things don't work out.
