+1 on the pygmies. Cutest things ever and wonderfully suited for a ten gallon. If you do want one of the larger species, I would go with pandas, as they stay relatively small compared to things like bronze cories.
Do make sure you have a nice smooth substrate. They don't work well with large gravel, either, no matter how smooth it is, sadly.
Like others have suggested, the cory cats are fine (whatever kind you may choose), but the cherries won't do well at all with a betta and cory cats since both of them will eat the shrimp if given the chance(when they are molting/baby shrimp). Unless your tank is densely planted with lots of hiding places, the cherries will always hide and eventually they will die off. So I suggest just getting the corys with the betta.
I have a breeding colony of RCS with a trio of panda cories and six female bettas. Haven't lost a single one to any of the fish. My tank is very densely planted, it is true, but my shrimp wander around stealing food from under the cories' noses and landing on the bettas' faces, out in the open. Bubs and adults all gather in the open space at feeding time, especially.
This may be unusual, but just to let you know it works for me. :)
Its the densely planted part that is key or lots of hiding spots because I have them in every single one of my tanks at one point and I don't lose any in my heavily planted tanks but the numbers dwindle in my other tanks with less covering, all started out with 20 or so, some have more, some less, and some have none.