For the shaving cream prank listed above... instead of a 9x12 envelope get paper bags from grocery stores. You know the ones they used to use all the time before plastic. they are bigger then the envelope and therefore hold more shaving cream. They are also pretty strong and usually hold up fairly well.. just ask for a couple extra next time you go to the store. Also with those since they fold flat you dont have to seal it up... you can just stick the entire edge under the door. the idea is to do this when they are gone and do it several times so there is a ton of shaving cream in their room when they leave.

Another good one we did when i was in school was to take the giant moving carts that alot of dorms have for when students move in. you get some rope and tie one end to the cart and one end to the door knob. The carts that we had were so tall(think like bellhop carts at hotels) that if you laid them sideways they were wider then the door. the key is to get the rope really tight so that they cant open the door at all. When they try to the cart just slams againt the wall and they are trapped in their room.

Also, alot of dorm rooms have tile floors and students buy big carpet pieces to cover them up. A good prank is to just keep sneaking random substances like mayo, slices of cheese, yogurt and put it under their giant rugs. in a couple of weeks it begins to smell real bad and they cant figure out why. plus when they finally lift the rug up its a nasty mess to clean up.