Bettas can do okay in community tanks, but its still kinda of iffey.
First you have a mellow betta, so he won't pick on anyone else.
Second sometimes the other fish will pick on the betta, those fins are tempting, and with the water current and the other fish being faster sometimes they have a hard time getting food.
Heres what I am thinking of doing with my 20gal when I get home from college.
5 cories - The smaller ones, such as spotted. If you wanted to go with drawf or panda cories, you could have say 7.
6-8 tetras - You have alot of choices here, I just wouldn't go with the really big tetras such as congo or the other large ones. But anything from neons, to black phanton, even silvertips all stay a nice size.
A trio of a non-schooling fish. You could get cherry barbs(1M/2F) a trio of male platies(so you won't be over run with babies) You could also do male guppies...but they may get picked on, and its hard to find good stock these days(atleast in the US anyway) but you could always try.
A as your center piece fish you could go with a honey/dwarf gourami. I have a honey in my tank right now, and I love him.
These are just of course suggestions to get you started.
