I think in the land of email, blogging, facebook chat, and texting the importance of letter writing has seemed to slide to the side. I think it is so, so, SO important to still teach this skill. Every year in my class we write many letters to friends, relatives, and businesses. The students love getting a response back. You should see the first time they try to write on an envelope. YIKES! I just loose a little bit of hair that day :)
Anyway here are two online interactives to help students learn a little about letter writing. After doing these, they had no trouble carrying the knowledge over to using real paper.
BBC Letter Writing
Read Write Think Letter Generator