Yes, there are some really good free games out there and many of them are free.  Try a few of these below.

Kyodai Mahjongg

his has much more than a bunch of Mahjongg variants.  Plus it has several other games that will get you addicted and infuriated at the same time.  I have had a great time with this program for a couple of years now.  Try it and see if it doesn't take up a whole lot of your free time

Royal Cribbage

I enjoy the card game cribbage a lot.  Royal Cribbage is a tough competitor.  It beats solitaire!

Steel Panthers: World at War

I couldn't let this section go with out at least ONE wargame mentioned.  And this is a doozey.  A great game with tons of historical scenarios on WW2.   It plays well even on slower machines.

 Many others are available all over the web, but be careful where you get them.  Many are only a door way to spyware and viruses. Online games are especially bad about this.  Only work with major sites... Microsoft, Google, Yahoo, Downloads.com, etc.  You'll never run out of things to do. 

You might also check for "Abandonware".  These are software that are no longer being sold. Though most are a bit dated, there are some great stuff.   And, if the company is no selling them, then you using it certainly costs them nothing in potential revenues.  But, again, be careful and check out the sites by looking for reviews.