My favorite flash game, ever, is undoubtedly Space Skirmish 2. I'm not sure if I should say any website in particular created it, but you can find it if you search it. It is extremely addictive, and the best flash game I have ever played.
My favorite is Shift 3. Because there is a lot options in the game like you can build your own map with many different tools like doors and gravity shift and so on.
