Free Rice - for each answer you get right, the site donates 10 grains of rice to the United Nations World Food Programme
Find links to great Math, French, Socials and Science games and websites at Safe Kid Games.com. You'll find links to Japanese, Mandarin and Spanish games as well!
SKOOLBO This is a great educational website I've recently found out about through some other teachers. They have spoken very highly of this site and I have seen the children in their classes fully engaged in the educational games. Once you register your child on the site (absolutely free) and he or she starts playing the games the software automatically adjusts the level of difficulty for your child based on the answers he/she is getting correct. That way the children are always on an appropriate level based on their abilities. I have linked you to the "About Us" page.