I recently found this list of RFCs on my computer. They're slightly old, so they don't include some of the newer April 1st RFCs, and I'm fairly sure it's incomplete, but it's a list of some of the old April Fool's Day RFCs. Some of them are actually funny! :)
You may have read about how Slashdot has upgraded their site to use CSS, which allows some degree of custom styling. Well, I've mucked around with their CSS, and came up with the following userContent.css addition:
Pandaren Xpress - Too Lazy to pick up the Phone? - WoW's answer to EQ2's /pizza command. Water on Mars - a picture of water on Mars. (The picture is actually real, too!) Slashdot | - OK, so they overdid April Fools Day yet again. But this one was actually funny. New England Suffers Maple Woes - from All Things Considered. It's not available online - yet - but it's really amusing. Had me going for a bit, until they got to Exploding Maple Trees.