Here is where you can come to post obscure, forgotten, interesting, or must-play flash games.
I'll start with a few well known games that I consider must-plays.
http://www.newgrounds.com/portal/view/592473
If you spend anytime on Newgrounds you've probably played this, but I'm putting it here just in case. The most impressive factor in this game is the animation; it feels as though you're actually directing a Madness Combat flash. It also features skill and attribute customization and progression in arena mode.
http://www.newgrounds.com/portal/view/575163
A chaotic fighting game. The simple mechanics mask a deep environment to interact with. There is never a dull moment. That was a pretty awful sales pitch, so just play it. The controls are kind of funky but you can change those. Note that its not intended to be fair; just fun.
http://www.newgrounds.com/portal/view/541333
A beautiful and atmosphereic exploration based game centered around discovering the story of a long past civilization.
http://www.newgrounds.com/portal/view/519030
A quirky art game with a very interesting mechanic. Its difficult to summarize, so I suggest you just click the link.
http://www.newgrounds.com/portal/view/592911
Its the Besterest!
http://www.newgrounds.com/portal/view/580377
I know most of you are probably tired of zombie games, but this is worth it. It isn't often you see a side scrolling RPG of this quality.
http://www.newgrounds.com/portal/view/598023
The translations are bad and the plot isn't terribly exciting, but the gameplay is superb. Just about everything in the environment can be used to your advantage.
http://www.newgrounds.com/portal/view/593397
An artsy platformer/puzzle game that you should play cuz' I said.