I started getting to know the founder of Ramo Games a few months back, right around the time when they were really expanding their content. They're a great group of people really trying to make a difference in the lives of kids. I highly recommend their site, not only as a place to find just about any educational game you could ever ask for, but also as a safe place to send your kids. They have a really nice blog too. Perfect for teachers, parents, and children alike.
I have been using this site the past 2 months since a friend who is part of my PTA suggested it. I love it because it is a comprehensive directory. I make my 7-year old only play games in different categories (history, math, logic) depending on where she needs the most help.