"Picturing"

This is a great prank for college or high school students.

When the person walks in to his room, it is covered with hundreds of pictures of a girl he has liked "secretly".

Be ready with the camera, because the pictures of him being surrounded by hundreds of pictures of her will be priceless!

Supply List
1-2 rolls of scotch tape
hundreds of photocopied (or for flair with those of you with lots of $) color printed pictures of a particular girl. (The girl picked is key in this prank.)

Plan
Take your supplies and enter the room and lock it. Quickly go to work. You will need multiple people if your time is short.
The plan is to entirely cover every inch of the room. Start with hanging dozens of photos from the ceiling. Cover all of the walls, all of the furniture, you can even cover the entire floor. I personally would leave the outside of the door alone to add to the surprize factor, but covering the inside of all of the drawers and putting photos in all of his books is a nice touch as well.
For bonus points make large prints for the windows (make sure the picture if facing out.)

A web cam set up in the room facing the door and his look would also make a nice addition.

Cost saving tip
Make the photo copies at the computer lab. If there are photo limits, get 4-5 friends each to max their daily limit for a week or two. That should get you more than enough photos.

Goldfish Cupping

This is an funny and innovative twist on a classic prank.

Imagine them opening their dorm room door to see your entire floor covered with cups containing water and a goldfish!

Materials
Enough clear cups to cover the entire floor
Lids for each cup (so you can stack the cups in the ice chests)
A couple large ice chests
Enough goldfish to put one in each cup
A net
A team of helpers

Plan
Step 1. Buy the goldfish. It might take a couple stores to get enough. (Don't wait too long or the fish will die).
Step 2. Fill this ice chests with prepared cups (with water, goldfish, and lid)
Step 3. Carry the ice chests into the person's room and shut the door
Step 4. Start in the far corner and move your way toward the door (If the door opens inward, make sure to not put cups where you can't open the door!) You may have to leave and refill the ice chests a few times.
Step 5. Leave with all evidence and wait for them to come home

Pro's of this prank
In addition to taking a really long time to empty each cup, the added goldfish complicates matters. Will they simply flush hundreds of live goldfish? Will they try and save each one? The room is totally unusable until the matter of the cups are dealt with.

Con's of this prank
The cost of goldfish can add up. If you are short of cash, try just putting a few goldfish in the cups nearest the door and baby carrots in all of the other cups. On first impression, it will hopefully still look like a room full of goldfish.