Files can range from lesson plans, to classroom signs, to fun and exciting projects (ATP and I used this end of the year celebration last year) and had a blast with it.
I am so excited to have sold my first product on TpT just this week. I am still VERY, VERY new at adding products (one of the summer goals I didn't quite get to), but it seems like a great way to make a few extra dollars off of items I have already worked on creating. Check out my file "Incorporating the Arts into Writing" here.
Let me know if you find other good stuff I should look into.