http://www.newgrounds.com/collection/xiaoxiao

Xiao Xiao, not all are games, but always a classic.

http://www.albinoblacksheep.com/games/castle

Defend Your Castle, one of my favorites from the days of 99 =P

the flash game I spent most time with

http://www.candystand.com/play/vector-tdx

(tower defense game)

Only flash game that matters

http://www.newgrounds.com/portal/view/534416

I love this one too ಥ⌣▽▽∇_⌣⌣ಥ

Definitely a good game.. Not sure what the stuff after your message is. heiroglyphs!

http://www.newgrounds.com/portal/view/445366
Puts all other flash games to shame.

My current addiction:

http://armorgames.com/play/7348/corporation-inc

Not necessarily a flash game, but if you are camping something and just want a game to pass the time this is a great game.

http://www.i-am-bored.com/bored_link.cfm?link_id=12114

http://www.funny-games.biz/defender06.html

Best game ever.