Kongregate and Achievements
For the past few weeks whenever I've had a free minute or two I jump over to Kongregate and check out new flash games. I barely ever visit other flash game sites because Kongregate has a persistent log-in system, chat functions, and achievements which the others lack. I love achievements and finding them on a flash game site has made me extremely happy!
Whenever I need a new game I go into the menu for badges (badges are what achievements are called on the site) and pick a badge from a game that I've never played before. They don't give out badges to every game, so most games with badges are decent. It's kind of like a Kongregate stamp of approval. They aren't all winners, but it's a great way to find new games without sorting through the 30,000+ games on the site by title alone.
Not only is it a good way to discover new flash games, but I love achievements for the sake of achievements. I know that some people think they are simply a measure of e-peen, but the reason I like them is because they get me to play videogames in new and interesting ways. Anything that pushes me out of the box and simultaneously adds more gameplay options is a good thing.