There are a couple different types of fish you could keep with a betta.
If you want something that's not too large and with character, try a single angelfish. I keep my common juvinile female angelfish with my female betta's usually, but sometimes put her with my male betta's to keep them company.
Don't put a black lace in though, I haven't yet tested them out with betta's.
However, you could try some live-bearers such as mosquito fish, fancy guppies, blue limia, mollies (preferrably black ones), werry widow or platties. Colourful and active little fish, no harm should come to your betta or any of these little fish, cept maybe the guppies, cause of the tails and all.
You could try couple types of barbs aswell, black ruby barbs are lovely fish, chequer barbs, golden barbs, tiger barbs and cherry barbs. I haven't tried them with betta's myself, attempted to try one my old my male betta's with tiger, moss green and chequer barbs in a comunity tank a couple year's ago, Cherrish, beautiful little cream coloured betta with red spots over him. I didn't count on my eel-tail catfish eating him after only one day though. Was not very happy.
I haven't tried betta's with barbs since that incident, purely because I usually keep barbs in the comunity tank, but I only have a few weeks till I get another tank, so maybe try it then and let you know?...
Though, maybe try balanteocheilus melanopterus, labeo bicolor, labeo chrysophekadion or labeo erythrurus, aka, silver shark, red-tailed black shark, black shark and red-finned shark. Silver shark gets a bit big, but all of them are hardy fish and mind their own business. Harlequins are peaceful little fish, so maybe few other those??
Okay, I think I've prob given one the largest recounts of fish ever for betta's. The only other fish I can think of are lyre-tails, argentine pearl, clown loach, paradise fish, dwarf gourami, dwarf rainbow cichlid (pelmatochromis kribensis) and ornate dwarf cichlid (apistogramma ornatipinnis)
Haven't had all those fish, but have read about them alot and have a friend who breeds a few of them now. Most are small, colourful, active fish and will prob do alright with a betta. Most swim about mid-water to the bottom of the tank. Some do swim at the top of the tank like the betta does and I think the mst aggressive is the paradise fish, so might have to check on that.
Hope that gives you some ideas for what you want in your tank with your betta.
Good luck
Brachygobius aggregatus and Brachygobius xanthomelas are a few of the nine existing species that do not need brackish water conditions to thrive. I kept the Brachygobius aggregatus with no problems at all in totally freshwater setup.
