There are tons of free games available on the internet, below I have listed a few of them.
Ability- Java games of strategy and skill.
Bingozone-Play games and win cash and prizes.
Bingoonline- You can play bingo and win points that can be used to buy great prizes.
Grump Ventures- Cool Solitaire style game.
iWin- Get icoins for playing games. Redeem the icoins for prizes.
IWon- Numerous ways to win money.
MSN Gaming Zone- Play one the tons of available games.
Riddler- Riddles, trivia, crosswords and more.
UpRoar- Play your favorite TV game shows, plus many other cool stuff.