who? mr williams? well, lets put it this way: he's the only one and his puffer is a baby mbu.
basically, the vast majority of the puffers that grow too large for an oscar to eat are nasty, bitey fish and would do very bad things to an oscar. some mbus can be trusted around other fish, but they are largely the exception. however, mbus can easily reach and exceed 2ft in length, which means that one would need a very large tank indeed.
really, mixing any fish with a puffer is something of a gamble. puffers can be quite unpredictable and you can never be 100% sure that yours won't suddenly decide to eat his tankmates. the most reliable puffers are the ones that you can pretty much trust to bite things!
the only puffer that i would feel comfortable keeping in a fast-swimming, semi-aggressive community is the South American Puffer (or SAP). they can be fin-nippers and aren't to be trusted around anything smaller than a guppy, but SAPs generally lack the territoriality displayed by other puffers. however, i have yet to see one grow any larger than 3 inches long and 1 inch in diameter. this means that the SAP is still snack-sized for most of the larger cichlids. also, because SAPs display little interest in claiming a territory, they also fail to recognize the territories of other fish. because they aren't the fastest of fish, this makes them a target for the territorial aggression of other fish, which means that SAPs are not compatible with most of the smaller cichlids either. something with low aggression such as German Rams or Keyholes might be an option, but even then you'd need to keep a close watch on things. definitely avoid any cichlids with long fins such as Angels. i had Kribs with my SAP for about 3 months and he quickly bit off all their filaments, although fortunately he didn't keep going.
word in the oddball forum is this: don't keep it with your puffer if you would be sad to see it eaten. given the friendly, dog-like personalities of most oscars, i personally would hesitate to try an oscar-puffer combo and i certainly wouldn't recommend it to anyone. but each to their own; some people decide that these sorts of things are worth the risk.