another high school librarian
I have (HAD) the same problem as you. Most ideas I've found are too young for my high school readers. However, recently when doing a search on amazon.com I found a wonderful bulletin board idea book for secondary students. It's called "Look Again! Appealing Bulletin Board Ideas for Secondary Students" by Judy Serritella. The ISBN # is 1586830538 if you would like to do a search. I've found many ideas and don't know where to start with them all. I sure hope this helps you. Let me know if you find it!