I have a bit of a problem with all the so-called 'free' game sites out there. While most of them do offer games that are completely free, the games are usually just little samples that you can play for an hour or so, and then you need to buy the game. And while I have no problem buying a game if I enjoy it, why call yourself a 'free' game site if your games aren't actually FREE?
My solution, generally, is to play browser-based games. Downloads usually require you to pay for something down the road, whereas browser-based stuff almost never costs a penny. More, they can be played straight out of any browser you like, so long as you've got the right plugins installed, and won't take up valuable space on your computer (nor will they install weird software that'll get in the way of speedy computing, like many demos do).
Here's a listing of some of my favorite browser-based sites for your perusal.
1.) Billy vs. Snakeman. I've mentioned this a few times in my articles before. What can I say, it's fun. If you're an anime fan you'll enjoy the weird references, fun team-based game play and crazy amounts of content. More, it'll last a lot longer each day than your average browser-based entry.
2.) Urban Dead. Again, usually pops up when I mentioned Billy vs. Snakeman. You have to run around a city full of zombies and try to survive. What's NOT fun about that?
3.) Free Tetris. You play a clean, Flash-based version of Tetris. There's very little that can go wrong with this, from my point of view. I love breaking Tetris out for those long, boring classes.
4.) Newgrounds. This site is chalf full of crazy games to play. Some are hilariously good fun, some... well, some aren't quite so much. It's an enormous hodge podge of different genres. Look around for a while and chances are good you'll track down something to your liking.
5.) Free Online Games. Titles don't get much easier to remember than that. Similar to Newgrounds but more to the point, Free Online Games is another giant repository of Flash titles. Some are good, some aren't. I tend to prefer Newgrounds since there's mroe variety and new games come out on it more often - plus the layout looks a lot better - but if you don't mind an older, utilitarian experience, give this place a while.
6.) Desktop Defense. A nifty little game where you try to keep a slew of enemies from getting to the other side of the screen by setting up defensive towers. It's a really neat, if frustrating, experience.
There are probably hundreds of sites out there with free games, but I can at least assure you that the ones above won't mess up your computer in the process. They're relatively ad free and don't have those annoying pop ups which plague our most horrid dreams. Look them up, give 'em a whirl and enjoy.