There's nothing more depressing than a sterile dorm room. Its true that most people I know have more trouble with clutter than a blank slate, but I know of the occassional room where everything simply MUST have a PURPOSE. Its true that it can be difficult packing everything you need and everything that makes you feel at home into your tiny Prius to treck thousands of miles from home, but realistically a $4 (or $20) poster, stuffed animal, or whatever can make all the difference. I personally think every dorm should have at least one (offline) photo, lest you appear Dexter-like, or at the very least put your peeps on your screen saver. Sometimes life sucks and its important that your room makes you happy and not remind you of a prison.
Besides, when you invite someone into your room, you'll appear quite lovable with a WALL-E at your desk. (Who could say no to a face like this? You'll at least get some pizza out of the deal...)
A word on poster selection (that time honored constant of dorm decor): Put up whatever poster you happen to like. Whether its a landscape or your heroes, within reason, ignore your roommate....
even if you are in the heart of Republican teritory. Just put it on the inside of your closet door.