Like Digg, StumbleUpon has a healthy contingent of users that play and read about games (incidentally, I stumbled upon StumbleUpon when I was glancing at Joystiq's traffic referral links), so the suggestions in the video games category are generally excellent. You can try out a demo of the gaming section by clicking the link tagged "online games" which will provide you with an endless stream of direct links to flash games that can literally take up your whole day.
If you're looking for a more passive experience, the toolbar also allows you to browse randomly through video game links in categories such as news, video, photos and even Wikipedia pages. One moment you can be reading about the history of gamepads, the next you can be watching the latest footage from Crysis. Random selection at its best.