Cleaner wrasse, ribbon eels, regal angels, certain butterflies....a great white shark has been kept successfully...so far - the aquarium in Monterrey, CA has one. I believe they've had it since 2003 and still have it. I do want to make the drive up (8 hours from where I'm at) just to see that...
EDIT: Okay, the Monterey Bay Aquarium somewhat has kept a white shark successfully - but it was never on display. For some reason, I thought it was. They held a 5-foot long juvenile great white in a five million gallon holding pen in the ocean for a week, and at the end of the week, recorded the first confirmed feeding of a great white in captivity. The shark ate. Now they are testing longer periods of shark captivity and transport simulations to the aquarium for future possible display.