42explore Thematic Pathfinder-another free resource for teachers! Here is the description from their site:
Why start with a search engine, when you can find a pathfinder to fit your needs at 42eXplore? When learning something new, it's nice to have more than one resource to explore. This web project provides "four to eXplore" for each topic. On each page you'll find definitions, activities, the 4 good starting points, and many more links and resources for the thematic topic.
If you are looking for specific sites for a topic and you are an elementary teacher, I encourage you to check this site first to save you time! You can search by subject or click Topic index to see a list of all available.