The dwarf puffer is considered to be one of the biggest a-holes of the freshwater community and are definitely not community fish and are best kept in a small species setup. Some people do keep them in larger community tanks with success, but it is not recommended. Dwarves are vicious little critters and will nip the fins off just about any other fish. They are capable of killing tank mates much larger than themselves with their relentless picking and nipping. Also, their small size can cause them to be eaten by larger fish. If you're going to keep dwarves, plan to provide them with their very own tank. There are a few tank mates that can be successfully kept with dwarves, though, and are worth mentioning:
Otocinclus - Known as "otos" in the aquarium trade, these little guys are an excellent addition to a dwarf puffer tank. Almost everyone who has tried them has successfully kept them in a dwarf tank with little to no problems. They remain small and do not attract much attention to themselves.
Shrimp - It's basically a gamble with shrimp. Some dwarves don't even notice them, while others will rip them to shreds within minutes! I have had a great deal of success keeping Amano Shrimp with my Dwarf Puffers so far, but I know that as soon as the puffers find out the shrimp are tasty, that will be the end of their peaceful coexistence! I would suggest buying some ghost shrimp from the local fish store and giving it a shot. Ghost shrimp are a very inexpensive feeder food, so if your puffers eat them, you're not out much money and the dwarves have gotten a great meal out of it. If they don't eat them, then the shrimp will make an excellent "cleanup crew" for your puffer tank.... scavenging the bottom and cleaning up any leftover food.
You are left with very limited options besides other puffers. I have seen a few tanks where ppl have gotten many different species of puffers and kept them all together but that was at least a 30 gallon tank.
Hope this helps