I just want to add that you can never guarantee no violence. Some bettas are lovely community fish, others are murderous fiends that will brutally destroy any and all tankmates.
Cories are always the safest place to start. For a ten gallon, I would recommend either pygmies (there are 3 pygmy species) or pandas. Pygmies are extremely cute and stay tiny. Pandas are normal sized, but do remain smaller than the other types, like bronze, emerald, peppered etc. However, they are pretty sensitive.
Because I'm a massive believer in making sure active fish have all the room they need and love to swim, there is a very limited number of species I would actually try in a ten gallon. Basically, if it isn't on this page, I probably wouldn't go for it: http://theaquariumwiki.com/Stocking_a_10_Gallon_Tank
. This is just my personal preference, though; many people have success with species not on this page (such as neons). I just like to give them more room. :)
My favourites for a betta tank:
- one school of 6-8 ember tetras (absolutely gorgeous, internet pictures do not do them justice; peaceful, not nippy at all; very chilled so no frantic activity to stress the betta, but still capable of getting out of his way. I have 10 in my sorority).
- one school of 6-8 pygmy cories (most bettas do well enough with bottom dwellers)
- shrimp (shrimp are just the bomb).
If you don't fancy or can't get embers, 3 Endler's Livebearers (male) would work with a relaxed betta. Alternatively, microrasboras such as borasas maculata and borasas brigittae (I have these) are very pretty and so small most bettas will completely ignore them.
2 ADF would be a nifty alternative to other fish, if you fancy them. :)