Not all puffers are psychotic maniacs. I've kept the brackish to marine species Arothron hispidus with scats and monos without any problems at all. In my soft water aquarium I have a South American puffer that gets along fine with cardinals and other small fish. It is a bit bullied by a ram (Mikrogeophagus ramirezi), and the glassfish steal its food, but otherwise it's seems to be happy and healthy and has been there for almost a year now.
I have a theory that the aquarium itself is a factor. In the wild, puffers live in complex habitats, and when you watch them, you see that they are constantly swimming up and down rockwork, plants, and so on. Last summer I spent some time trying to catch some North American estuarine species in Florida, and it was fun to see that how they live, and how we tend to maintain them, is completely different.
So, my theory is that because my tank is busy (not overstocked, but with lots of small fish at every level) and filled with plants and rocks, the puffer has to work to find its food. Most of the food gets stolen by the other fish, or the puffer gets pushed away from the feeding area by the ram, so the puffer has to hunt for bits of food that the other fish have missed. This reproduces more closely their natural lifestyle, which doesn't involve having choice items dumped in front of them! In the wild, they are constantly nipping at plants and rocks and oyster shells hoping for a morsel of food (hence the fast-growing teeth).
There were some species that got fin-nipped, and those were removed, so what is left is stuff that is either too fast (tetras, glassfish, halfbeaks) or able to respond in kind when annoyed (ram, Panaque, upside-down cats). That seems to work. One advantage with the South American puffer is that is relatively peaceful to begin with. It is also nitrate-tolerant, so you don't need to be paranoid about overstocking the aquarium.
That said, I keep my male + female (not yet a pair!) red-tail, red-eye puffers in a 33 litre tank with a trio of Otocinclus. I'm not quite ready to risk keeping these in a community tank yet!
Cheers,
Neale