I found a site in my Women's Day magazine that has over 5,000 free softwares to choose from.
Here are a few of the games they have that looked interesting:
1. Armand & The Foppish Hat: Armand and the Foppish Hat is a short adventure game in the style of the classic NES and SNES Zelda games. It's a silly story about a heroic, but slightly pompous, swashbuckler whose favorite hat was stolen from him on his way to a party. Since a gentleman obviously cannot be seen without his hat, Armand must track down the thief and bring him to justice.
http://jhanson.com/software/armand.html
2.Knytt Stories:In Knytt Stories, each level is its own little adventure, one level is included with the game, where you have to stop a machine that draws the life out of the planet. An official expansion pack is also featured at the website with four original levels.
http://nifflas.ni2.se/index.php?main=02Knytt_Stories
3. Galaxy: Galaxy is a game based on Masters Of Orion or Galactic Civilizations or any number of space exploration and colonization games. Each time the game starts the galaxy is randomly generated so no two games are the same. You command the Artean Empire and must expand the empire to control the galaxy. Your one obstacle is the Rho, an alien race of cold blooded killers.
http://24xliam.tripod.com/galaxyseries.html
There are many, many others to choose from in different categories.