If you keep an eye out for colorful postcards, you can create an intriguing piece of wall art that will grow over the course of the semester and be a nifty reminder of all the cool stuff you've done. Best of all, lots of promotional postcards (which advertise a new band, movie, gallery exhibit, whatever) are free! You can find them in bookstores, record stores, and coffeeshops, or even on the street. Also, if you're feeling super-artsy, you can cut up local newspapers and/or magazines and make collages to beautify your space.