I once pulled a decent prank on my older brother.
Several years ago, when he had moved out of our parents' house into his own apartment, he left behind his Playstation 2. After a while, he had asked that I send it to him, being that it was indeed his. I didn't actually have a problem with this, but I recognized this as an opportunity to mess with him.
I went to my closet and pulled out the box in which our old Nintendo 64 came. I took out the styrofoam pads that packaged the Nintendo 64, grabbed a knife, and carved them until the Playstation 2 and controller would fit into them perfectly. From here, I stuck the controller and console into these re-fitted styrofoam shock absorbers and slid them inside the box, giving it a solid feel and nice weight.
I then grabbed a large plastic bag (of the Zip-Lock variety) and placed within it all the Nintendo 64 games, controllers, and accessories we had. I then taped this filled bag to the outside of the N64 box, as well as a note that stated (and I'm paraphrasing), "I don't want to give up the PS2, but I'd be more than happy to get all this N64 stuff to you."
Inside the box with the console and controller, I had also placed a small note with a hand with its middle finger extended drawn on it. I think I also wrote on it something to the effect of, "Just kidding."
Then I sent it to him, and it got quite the reaction.
It delighted me to know that my prank worked on him as well as it did, though I gloated about it working afterwards until it stopped being impressive and became annoying.
Looking back, it wasn't too bad of a prank.