Google Earth is a fantastic resource that will be covered later in this wiki. Even before Google Earth, there was a company called ESRI (Environment Systems Research Institute) based in Redlands, California. This company still exists and is not only a leader in GIS application but is also dedicated to K12 education. GIS (Geopgraphic Information Systems) can be integrated in science and social studies, as well as in mathematics and art/design. It also connects with GPS (Global Positioning Systems) to provide engaging adventures for students. GIS provides a foundation for interdisciplinary projects that allow for connections to the real world. Working with GIS also allows today's students to develop 21st Century skills relating to computer literacy, problem solving, communication, collaboration, and presentation. Using GIS opens the doors to occupational fields that are growing and in demand for students upon completion of their schooling. Most resources from ESRI are either free, very low cost, or available through an ESRI grant for K12 educators and students.

This link will provide access to the ESRI Main K12 Page in education

This web page provides a format that educators can use to collaborate and share lessons and techniques that are successful

A listing of over 250 lessons available for download using ESRI software

Free Download of Arc View for use in education

Most recently I came across four books (Our World GIS Education ) that were developed for K12 education. These books are available through ESRI at a retail price of about $50.00 each.These same books can be found at Amazon about $10.00 cheaper. The books do an excellent job of providing teachers with lessons and units that are based on twenty-first century skills and project based learning. They also include two CD in each book. One CD gives free access to necessary ESRI software for 365 days on up to 50 machines. After the 365 days schools can buy a site license for the entire school (about $500.00) or, better yet, engage students in an activity that provides the license for free. The other CD provides all lessons and support files for the book in a digital format.

Our World GIS Education Books - Winner of the 2008 Geography Excellence in Media (GEM) Awards by The National Council for Geographic Education. Books are presented as levels going from level 1-4 below.
Note that each book provides a description along with links to Workbook Support, Teacher Resources, Podcast with Authors, Taking a Look Inside which includes Table of Contents and First Three Chapters, and, of course, a link to buy the book.
Thinking Spatially Using GIS
Mapping Our World Using GIS
Analyzing Our World Using GIS
Making Spatial Decisions Using GIS

How about a free site license from ESRI? Visit the ESRI Community Mapping Page and get your students involved.
On this page you will learn more about Community Atlas and the grant program, have an opportunity to visit winning Model Projects from each year, download the Community Atlas instruction pages and model projects, explore all student projects, and submit or edit your project.