A couple months ago I joined a homeschool group on facebook and am now addicted to it!  This group hosts all kinds of fun swaps--penpals, geo boxes (fill a box w/stuff from your state/country and swap with someone from another area), flat travelers (based on the Flat Stanley book series, you send your flat traveler around the world and the host family takes pictures of your traveler doing different things there, most people also send info back about their state/country), and postcards from around the world.  These swaps are an excellent way for children to learn geography and we will be using the information we are collecting to start studying the 50 states this year.

This is the name of the group: Homeschool penpals/postcard exchange/geo-cac/book exchange/activity bagswap.  I highly recommend you check it out.  You do need to be a homeschooler to join and it is a closed group.

So far we have sent flat travelers to Alabama, Missouri, Montana, Ohio, Wisconsin, Canada, and Scotland. 
We have received geoboxes from Alabama, Arizona (coming soon), Lousiania, New York (coming soon), Canada, and South Africa (coming soon).
The only states we still need postcards from to have at least 1 from every state are: Minnesota, Rhode Island, Vermont, and Wyoming.  We have postcard from many countries as well but would love more.
When we receive things in the mail, we locate those places on a large map we have on our dining room wall.

If you can help with any of our geography studies please let me know. We can send postcards or information about Delaware in return.