Endgame319...
There are a vast number of possibilities here. It might be easier to tell you what NOT to get rather than to make recommendations of what fish you should buy.
You want to avoid fish with a habit of fin-nipping, specifically the barbs, like the popular Tiger Barb (
Capoeta tetrazona), puffers of any type, and some of the South American tetras. I once met a fellow who had an absolutely gorgeous
Betta that was ripped to shreds by the new, 'harmless' tetras that some dolt at his
lfs recommended for his tank. Unknown to him (and the
lfs salesperson), the tetras he had were the so-called Buck-toothed Tetra,
Exodon paradoxus, a notorious fin- and scale-eating tetra. Needless to say he was NOT thrilled with his choice of tank-mates for his
Betta.
If you want to stick with a tank that contains fish from the same general area as your
Betta splendens you might consider pretty much any of the commonly available
Rasboras, like
R. heteromorpha or
R. borapetensis. The danios,
Danio and
Brachydanio (Zebra Danio) will do just fine. I would personally avoid most of the gouramis because I've found that they have a hard time resisting those nice, flowing
Betta fins. Especially avoid the so-called Paradise Gourami,
Macropodus opercularis because they are very aggressive and will shred your
Betta in no time at all. You could add a couple of loaches
Botia as a clean-up crew. Avoid Clown Loaches though....they will out-grow the tank eventually.
I also recommend that you avoid cichlids of any type, including the dwarf cichlids. They are aggressive and territorial....too much for a
Betta to handle. Guppies, most tetras, killifish hatchetfish, pencilfish and a number of others will make good tank-mates for your
Betta as well but you should check your
lfs for the types that strike your fancy and then research their habits and behavior before you buy them.