I like (making, testing and occasionally creating) paper airplanes- especially ones that are slightly different.
I haven't tested it yet, but this link turned up in a Windows XP Secrets newsletter:
It might be the only one the author knows that flaps its wings, but it isn't the only one I know. There is one I used to fold and cut for my son, that is shaped and flies a little like a small songbird. I will have to see if I can actually write instructions for it and post it. I am not at all sure I can do that- that is, I am not sure I can write/draw the "how to's"..
If anyone has any links to the instructions for paper airplanes they particularly like (or origami, kirigami etc- other things I dabble at occasionally), I would be interested in seeing them. Post in comments or send me an email.