I'm bored by them this year. While I think
this and
that by google this year is really not very creative and also the traditional
one by heise lacks of serious plausibility statements I am really disappointed by the URL rotation at
xkcd. In my opinion this is just a bad example of surreptitious advertising for the two other comic strips.
Another bad example is
texy.net, I think one of the worst april fools I ever saw. The google
x-ray spy plan(googlesightseeing.com) also sucks, I could have done better with my gimp.
pirate bay's joke has at least a
nice image and it's also fun to see some people finding last years april fools like
this one (check archive.org).
I have to make one exception, the only creative one I saw this year is:
http://www.securitylab.ru/news/extra/349440.php
Not because of the actual content, but because of the reference (hint, check the URL) ;-P
The
strap-on wii-mote is also worth mentioning
A lot more are listed in a post in
nerdcore weblog.