ZWOK: You have teams/guilds/clans or whatever you like to call them. You get to create a little guy, this game is somewhat like worms. The more points you get you unlock different kinds of weapons. This game is also online, so you get to play with other people. There are 3 players per team and you try to eliminate all of them before you die. This game is actually pretty addictive when you get into it.
Desktop Defense: Probably my favorite of all, Desktop Defense. These little guys called "creeps" are trying to kill your desktop. So you build towers to prevent them from crossing over to your desktop. There are different kinds of groups. Normal Creeps, Fast Creeps, Group Creeps, Spawn Creeps, Flying Creeps, and the Boss Creep. Each one has there weaknesses and strengths. There are also six towers, Pellet Tower, Squirt Tower, Dart Tower, Swarm Tower, Frost Tower, and Bash Tower. There are also 5 modes, easy, medium, hard, challenge, and fun. You start off with 80 gold and 20 lives, gaining gold for each creep you kill. Check this game out it's really fun .
Line Rider: Very fun game and very simple. You simply draw a line, and have your sleder go down it. You may create curves and circles, anything to your liking. You may save your ride for later use. The only bad thing about this is that if you mess up once you can't erase that portion of it. You have to erase ALL of it. You can also download a screensaver for your computer
Penguin Hitting: Ever felt like hitting a penguin with a club? Well here you go the perfect game for you? Simply this yeti-like fellow has a club and you have to see how far you can hit it. Simple as that.
Bowmaster Prelude: Another great game to check out, you are a castle and you try to protect from your enemy. The farther you go the harder it gets. You also gain EXP, the more level you gain the more weapons you get.
3D Missle: One of my favorites to. You have to survive through the nine levels of tunnels. Sounds easy, but is actually really really hard. I've died many times before i actually reached the end, check this out for sure
Weffriddles: I RECOMMEND THIS GAME. You'l probably be stumped on every single level. There are like over 100 levels here, and you must figure out the answer. You have to try this out =P (It's not really a game, like a puzzle. You may also use their forum if your completely stuck.
That's a nice list of games i've never heard of. I like the ones that stretch and twist your brain through painful, but fun, strategies. It always makes you feel like you've accomplished something when (and if) you beat it.