K-5 GeoSource is a great resource produced by the American Geosciences Institute. On K-5 GeoSource you will find free lesson plans, science fair project ideas, links to virtual activities, and resources for professional development. The first time I looked at the site back in 2009 it had a distinct Web 1.0 feel. The site has improved of late to make it easier to find the materials you want. A few of the resources that I looked at were this free chart about types of rocks, a science fair project guide, and a short Geoscientist career guide.
Applications for Education
As I mentioned above, K-5 GeoSource isn't the fanciest site you'll find on the web, if you need to find some ideas to use in your classroom, K-5 GeoSource is definitely worth bookmarking. The most useful aspect of the site might be the science fair project guide that you and your students could work through to plan a hands-on Earth science project.