NotDoppler was my fav. technically the site still exists but the games don't work anymore. when I was in sixth form we had a commons room with computers and every lunch break I'd play the games on that site because it was the only flash games site that the school didn't block lol
I miss when StumbleUpon was good. I tried to go back to their new whatever-thing, and it just sucked. The internet changed too profoundly for it to survive, and its latter day mutations have not improved its viability.