Food Force is very interesting game and learning vehicle. Developed by the United Nations World Food Programme, the game helps learners understand the complexities of delivering food to those in need and the work of the WFP. A fun game that's a free download for Mac and Windows.
Comic Life is a great new tool that allows users to turn digital photos into comic books. I think this will be a wonderful creative writing tool. There is a free trial available for the Mac and it works seamlessly with iPhoto. I can't wait to put this into my student's hands.
Celestia is free 3-D space simulation. With Celestia, you can "travel" throughout the solar system. There are also hundreds of downloadable add-ons and list of educational activities, aimed at students in grades 7-12.