Lots more options out there though your betta and dwarf could very well go in there with either a trio of platies or maybe some ghost shrimp (won't always work with a betta) or with a snail or maybe some more frogs or you may want to try a few pygmy cories...
Anyway, look into killies for a start but only if you are prepaired for a challenge and do a lot of research first as there are many different kinds. Then there's shell-dwelling cichlids. N. multifasciatus is my favourite and the smallest - again, you need to research, research, research! A couple of dwarf puffers would work ok too - again though - RESEARCH!
Certain gobies and the badis as well... you know what I'm going to say
For more community-type set-ups, consider a school of 6 spotted rasboras with either 4 pygmy cories or a trio of mosquito fish. Alternatively, these would work with the fish I mentioned or in place of them - platies, guppies, honey gouramies (a trio at most), sparkling gouramies, a dwarf gourami, smaller cories and smaller loaches such as the dwarf chain loach or possibly a couple of kuhlies, golden dwarf barbs, small tetras such as neons, cardinals or rummynoses, otocinclus catfish, very small plecs such as bulldog or bristlenose, even some smaller cichlids such as rams can work in a planted tank.
Basically, the possibilities are endless and the key - you guessed it - is to RESEARCH!!! Don't make any rash descisions as you'll soon regret them. There are so many lovely fish out there and, the more you search, the more you'll discover and the more you'll keep changing your mind until eventualy you'll find something you realy, realy love. Then go for it
Good luck and have fun!