I'm not pulling any pranks (maybe), but I'll tell you some of the pranks that I've done or saw in college...
1) Between the time my RA went to take his morning shower and return to his room, his doorway was duct taped, and when he opened the door, nothing but crumbled newspapers, balloons, and other "filler" spilled out onto the floor. RA took about 15 minutes (though I swear they did it in half the time) in the shower and all, so this was a pretty good prank. Everyone helped out in cleaning the mess afterwards.
2) The more elaborate prank was pranking a roommate. Made a box long enough to cover his body, and painted to resemble the inside of a casket. Before he would usually wake up, Church music was played on a CD, and you could hear someone reading a final eulogy. He woke up thinking everyone was going to bury him alive. Nice way to start your day off, don't you think?
3) Professor pulled off a semester long prank by having on the syllabus on day 1, an exam for April 1, saying that it was worth 25% of your grade. When the exam was given, it was a simple "Fill in your Name and receive your 25% grade completion." Free pizza and drinks were handed out in the building's lobby. This was a lecture class, by the way.
4) Not an April's fool prank, but high school senior pranks that I've seen. Putting tires around the flag pole (literally! One of the girls borrowed a cherry picker from her dad's business to complete this prank). A rebuilt car inside the high school's lobby (without an engine, but emergency brake engaged, and pedal removed). Zip tied lockers on all student lockers. When the janitors began cutting them off and moved to a new hallway, other students would re-zip tie the lockers. This went on all day, with several thousand zip ties cut off by the final bell.