snails are great as long as mr betta doesn't nip at the antennae.
in a larger tank you'd have more options for tankmates, but for a 10 i'd consider pretty much any of the more placid small community fish. minimum of 5 or so if they are schooling fish. no long fins, flashy colours, nippy fish, or 'nervous' fish is what i've read, seen, been told for male betta tankmates.
when introducing any new tankmate(s) to mr betta's home, be sure to have an alternate place to quickly put any fish should you have aggression issues. have a rubbermaid container or some such at the ready, just in case.