Retro games rock!
Ok, hands up who remember's Tank Commander? I found a pretty good version here
Or Missile Command?
And who can possibly forget Pacman?
Or the even more classic Space Invader's?
All these games and many more are available using the Java plug-in. But it's not just Java that's good for freebie games. Macromedia Flash Player is another good programme that can be downloaded here with instructions on how to install it (the Yahoo toolbar is not needed).
With these two installed you should have access to a massive amount of free games from the just plain silly to ancient arcade games that forced me and many others into putting vast amounts of cash into big (sometimes small) boxes in my youth. Isn't technology wonderful? We can now play them to our hearts content for free. The only other one you may need is Shockwave (download and info.) another macromedia product.
With all 3 there should be no game you remember that isn't out there somewhere for free as well as alot more that you wouldn't dream of.
I'll be back later to edit my template and include links to my favourites - right now, for those space-sim fans, how about a bit of Defender (Shockwave) or Asteroids (Java)
Note: With Asteroids your pop-up killer may stop the game opening when you click play. If so, try right click and open it in a new window.