In the past my oldest daughter worked to collect postcards from each of the 50 states and then went onto collecting postcards from other countries. This was a great way for her to get some practical writing practice. The internet sites we used are listed in this post - Encouraging Writing through Postcard Exchange.
This time we wrote postcards to learn about formatting addresses, learn about proper letter/postcard punctuation and send a friendly note to a few people we haven't seen in a while.
Check out these great blog hops. They are filled with activity ideas for kids.