I'd have to say Jeff Pearson from Lucky's. He not only didn't pay his players or give them back their post up but he also fraudently charged their credit cards for over $200,000.
*luckily* I'm no expert on this - but NASA & SBG MUST be up there if you count all their scam contests with the sweet car - the apparently invisible ones (hmmm, maybe they're giving away Stealth Utility Vehicles