Word wall..this can easily be integrated into secondary classroom. For social studies, the envelopes can be various topics from the curriculum. Also include an envelope words that are used often in State Standardized tests.
DIY yarn organizer. It is great to facilitate the autonomy in the art center. Easy to store too!
Classroom Set Up - Encouraging Collaboration and Self-Directed Learning. This post if full of pictures and ideas. I love how there are so many different places for students to work, and everything is so inviting!