Students and teachers are always looking for educational games that they can access in school computer labs. Coolmath.com is a great resource for online math materials including a collection of great arithmetic, logic, and spacial awareness games.
These games are not only fun to play, but are mentally stimulating as well. Personal favorites include Bloxorz, Breaking Bricks, Castle Defense, and Math Lines.
Check out coolmath-games.com for fun games that kids enjoy playing that are also mentally challenging.