Game On: Increasing Learning though Online Games is a site by teachers that has resources, links, ideas, and games to use in education to help students get engaged and understand concepts.
The site has sections on why and how games are useful in education to help students learn and understand and then has educational games sorted by topic (Arts and Musics, Language Arts, Math, Science, and Social Studies) and by grade level under topic (elementary, middle, high school). There is even a section devoted to resources to help you make your own educational games.
The Science-High School games section has some great games, some of which I knew about, and a bunch that I never knew of. Each page has the link to the game, as well as a description of the game.
Game On is a great resource for educators looking to incorporate games into their classroom to help students get engaged, develop skills, and better understand a topic.
Related:
Mission Biotech - free, educational science video game
Educational Games - lots of them
Angry Birds Space and NASA team up for fun science
Roller Coaster Game as Learning Tool in Physics
Video Games as learning tools (Angry Birds)
35 Educational Games and Resources
