Here are the first three:
- Funbrain - One of the most popular educational gaming sites around. Not only does this site cover a variety of subjects, it caters to K-8th graders, and has nice teacher resources as well.
- Game Classroom - Excellent, safe, teacher approved, state standard aligned games for grades K-6. Also, lots of teacher resources to find such as: videos, lesson plans, worksheets, etc.
- Gameaquarium - A great site for games for kids K-6 in all types of subjects. Videos, eBooks, and teacher resources can be found on here as well.