I learned everything I know from Oregon Trail.

Oregon Trail. It was the educational computer game available in 1997. Or at least it very much felt like it with how many hours I played it in computer class in elementary school. But now there are even better educational games online! Like the one I found here.
Students love to be able to use the computers but things can get out of hand when they are done with the assignments and they need something else to do; such as pretending to be a colonist via this fun Jamestown-themed game. This "History Mystery" game is also a good one.

For you math teachers go here. There are enough games to fill up an entire year of interactive games.