Here are a few back to school doors I have discovered. I tend to decorate my bulletin board instead of my door to welcome the students back, but if you are the opposite, then hopefully these can help you.
Bright Hub used the students' names to create a word search on the door.
Adventures of the American Mind's art work is amazing! Check out a few doors she has used...
From Bulletin Board Ideas, here is an idea using crayons.
Scrap and Teach made created her bulletin board (yes, I realize it isn't a door, but it was too cute not to share!) using her Cricut machine and theme of Chicka Chicka Boom Boom.
Have a door or bulletin board you think I should see? Send me an email with a picture or leave a comment with a link so I can find and feature your idea!