There's billions of crappy flash games out there, and I've pretty much stopped trying to find decent ones myself. There are some good filtering sites out there to point out the decent ones like JayIsGames and LittleFluffy. There are also specific developers that make awesome games, like Orisinal and Eyezmaze (maker of Grow).
But for sheer quantity? This site takes it:
Nice interface with screenshots that show on mouse-over.
Fast load times, the games seem to be hosted locally on their server, no popups.
Some of my favorites:
N - for Ninja - awesome lode-runner like game
Holy Virginity - As Joseph, fend off angelic sperm from impregnating Mary!
Deanimator shooting zombies. Surprisingly hard.
and... so damn many more..