you guys forget or don't know the whale bet 7000btc per roll on just-dice, that's the story in 2013, and he rolled the probability of 96% win. that's insane
This one has to be the biggest bet made on any site for BTC at this moment. The ones that have been mentioned here have been overall wins and combinations of several bets. I believe PRC had some huge bets also some time ago (I think they were around 300-400BTC)