I have a few to contribute, sorry too lazy to link these:

1) decision 2: a cool top down zombie shooter game with cool weapon upgrades and whatnots

2) tontie (try to find the newer version), a finger/eye coordination game that requires a numpad, crazy hard and probably impossible to beat the higher levels, this game is pretty old, and i've been playing it for years

3) hack slash crawl, super simple but fun dungeon crawler

4) N, probably my favorite flash game of all time, a platformer/puzzle/timelimit/physics game where you have to jump around with your little ninja collecting coins that add to your time limit and complete stages before the time runs out

5) Cave story: not a flash game, but a freeware pc game that takes like half a minute to download, it has a cool story, awesome music and feels kind of like super metroid, and is about as long as super metroid too.