The technology world loves April Fools' day. Probably because so much of the "news" in technology lends itself to speculation (and let's face it, techies love to think about the "next big thing") the world of tech news loves to take advantage of this climate of anticipation and exploit it on April 1st. There's a freedom in this realm of culture that would probably cause a lot of trouble in other parts of the mainstream media; I've learned that, when I read through the tech news online on 4/1, I read with a skeptical eye.
Here are the funniest (and cleverest) ones I found this year:
PC Actor Charged with Assault. "How do you like them apples?"
Introducing G-Mail "Custom Time." A great idea for really messing with peoples' minds.
April Fools' Stories You Shouldn't Believe. A funny collection of non-headlines.
I'll add more if I see them.
UPDATE: two more...
Wikipedia, the online (and community-edited) encyclopedia, offered a fun spin on their regular "On This Day" piece on their front/main page.
You might also enjoy their fictitious front-page Article of the Day on Ima Hogg.