If you can find them, the freshwater bumblebee gobies (see my thread on DPs and bumblebee gobies for the latin name) are meant to be good. I believe the Minions have recently obtained some, though they are rather rare.
Other than this common suggestions are Bristlenose plecos and otos.
I have seen other who keep khulies and many things. I'm not sure how they go though. The general advice given is to get something that is pretty much inactive (at least during the day when the puffers are about) to stop the DPs taking too much interest in them.