Fuel the Brain is a nice collection of online mathematics games, interactive lessons, and printable materials for teaching mathematics. All of Fuel the Brain’s offerings are intended for elementary and middle school age students. In addition to the standard collection of games and printable materials, Fuel the Brain offers “seasonal” activities designed to correspond to the seasons of the Northern Hemisphere.

Applications for Education
Fuel the Brain offers a games widget that you can install on your blog or website. Rather than directing students to yet another website, you can install the Fuel the Brain widget and have them play the games on blog or website they typically visit for your class.

Here are some related items that may be of interest to you:
Five Sources of Fun Mathematics Games
Ten Problem Solving Games for K-8 Students
The Importance of Proper Mathematics