1. Kongregate
This is the king of all gaming sites simply because it turns playing online games into a game! You can score points, level up, complete quests and earn badges. Most of the popular games on the site allow you to play towards achievements. When you get these achievements you earn points and badges. It’s very cool playing a game with goals other than just completing it. There are also daily badges you can win and get extra points for. A great site if you are looking for all the big games and a reason to keep coming back.
Website: http://www.kongregate.com