Post any fun, addictive, and highly frustrating Flash games you’ve come across here. I’ll start by submitting N. A full version with user-submitted levels and a level editor can be found here.
Another great one I’ve found is called Bloxorz. Very fun.
Any others?
ARRRGGH!
Here’s a link to a thread I posted which in turn links to a site called Hecklerspray, which (among other things) posts links to some of the most annoying and random flash games I’ve ever had the misfortune to meet. Games like how many photocopies you can make of your butt before the boss fires you. A quest type game wherein you seek out items to damage yourself with in order to commit suicide at work. Irritating little flash kitty that you have to box in to win. There are new links every day and I still haven’t gotten to the end of the archive on this one. There is enough flash annoyance on this one site to cause heads to explode for millenia I fear…
So yeah, enjoy! 
hooray for N! Actually, the first link posted is to an unofficial, illegitimate web version someone hacked. It doesn’t run nearly fast enough or smoothly enough, and is only version 1.2 (way old). The creators are currently working on a better web version.
Here’s another link for N downloads:
http://www.thewayoftheninja.org/n.html
It also has viewable online highscore replays (click the ‘highscores’ link)! Very fun.
here’s my latest fave, Cursor x10. It’s one of those games that experiments with several previous ‘runs/lives’ – intriguing.
Which one? 
I made it to level 13 and gave up. I kept losing cursor # 1!
There’s an official SDMB Flash Game?
This one I can continue to enjoy.
There’s tons of good flash games on the Jay is Games site. My current faves:
and
I also love this game because it’s very similar to a game I invented and programmed into my graphing calculator in college
I’ve had fun playing online versions of Pictionary, Settlers of Cataan, and Roborally, but I don’t have the links handy…
I completed it but took me about 6 goes.
How much fun!?!?! I completed it first go too - obviously being a Satanist helps.
A game [Gimme Friction as mentioned by someone above] that is extraordinarily simplistic, yet effective. The designer’s intent is supposedly that you figure out the rules yourself so I’ll spoiler a very basic rundown of how to play for those who just want to get to it:
The cannon launches orbs. Once they stop moving, they expand until they hit either a boundary wall or another orb. You score points by destroying orbs; you destroy an orb by bouncing into it 3 times. If your ball bounces back below the dotted line, the game is over.
It’s a frustrating yet addictive game. After more time spent playing than I intend to admit, my high is a whopping 14. I’m sure one of you can do better. If those that do can tell me some sort of effective strategy, I’m all ears.
I introduce you to The grow games
There’s
Grow 1
Grow 2
Grow 3
Grow RPG
Grow Cube
Grow Island
They are absolutely addicting, they’re puzzle games so gauge how each affects each other and how long they take to develop to get them down.
By the way, Grow Island has two “complete” endings, each equally awesome, and I’d also say Grow 1 does as well though technically only one “wins” theres another sequence which I think is awesome (you’ll know it when you see it).
Also on the list (but not grow related) are
Cat With Bow Golf
Uh… something
Okay that last one is just messed up and I apologize for mind-screwing you, but it had to be posted.
Everyone needs to know about the site Jay Is Games.
Some of my current favourites:
Fancy Pants 2 (Sequel to the excellent Fancy Pants 1)
Sola Rola
The Dark Room
Darktop Tower Defence 1.5
Murloc RPG
OH! Also The Impossible Quiz
I’ll post more as I remember. 
Jragon that “Uh… something” game is awesome. Makes me think of something Radiohead would do, if they did flash games.