I always used http://andkon.com to play games... Site wasn't blocked at my old school so I just got into a habit of playing the site. ;D Unobtrusive homepage so it's nice.
JEEZ JUST LOOK IN THE FORUM BEFORE POSTING THIS. See the board right below this one? Kongregate? Yeah, well that undoubtedly has the best games, and a trophy/ranking system. digyourowngrave is nice also (again, has a badge system).
Armorgames used to be my favorite, but then our school got block-happy. Now I use notDoppler all the time Albinoblacksheep.com is a pretty good one that nobody has mentioned yet, too.
I always liked mofungames.com; not many poor-quality games on there, and many of them are really good.
I like kong but haven't been playing for awhile too many tower defense games and only a few good ones.
y not play at ijji.com teh yhave mmorpg mmo and there are the random games u can play its pretty fun actully and they have some pretty awesome mmorpg games like lunia u guys should go try it =P
addictinggames.com has some of the best! or you could just go to stickdeath.com and watch those funnies.
I usually don't stick to just one site... Addictinggames.com has the biggest selection, but if I see a game on there produced by somebody else (e.g., Armor Games) I usually head over to their site. I like to support the developers, and there are usually extra features ^^.
ijji and jippi are pretty good lol. funny names and good games You don't have to double post. There is an edit button which you can use. Also, this post was a gravedig. Check the rules out if you don't know what it is stickcricket is a classic always use to play it at school back in the days and still play it at work haha