Kongregate is a huge online community based around flash games. What makes it different for other flash games sites is quality over quantity. Most games listed are qorth trying (maybe except newly added games that are under moderation). Ratings allow users to rate any particular games and gives other players a way to tell wether a particular game is nice.
An added bonus is a chat system enabled for all games, some multiplayer (yes, one of the few sites with real multiplayer games) with different rooms for different game types. Challenges, Achievements and Badges would keep you coming back. 1-2 times a week, a new challenge would be annouced which dares you to complete a task in a particular game. By completing that task, you gain either 1 TCG card or a sweepstake entry (usually 1-2 tims a year). The card will entitle you to play the Kongregate TCG game (exclusive) on the site, collect the cards to expand your deck. Developers can upload their games to kongregate and can earh cash rewards if it wins the contest (monthly).
Badges require you to complete tasks too but instead of TCG cards, you gain points. Points allow your account to level up and move up the leaderboard. Achievements track your highscores and put them up on the server. So the scores arn't just on your computer, you can challenge your friends to beat your score too.
Try it out: Kongregate [be sure to register]
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I like Kongregate as well, although I think the selection of games is more suitable for men. For games that are more friendly for Female audiences I would suggest sites like Addicting Games and Chinese Gum. Both sites have a large selection and nice features.