I was just researching dates for a rather unusual calendar that I'm giving someone for Christmas (you can personalize it with anything you want) and I discovered some dates for 2007 that might be of general interest to this group.
February 10: National (International?) Plimsoll Day -- And I know just how to celebrate!
April 30 (USA): National Spank Out Day -- No idea what this is, but it sounds delightful. It also happens to be National Honesty Day, which might not be as good for some people.
These are the ones I found so far. Anyone else have any fun ones to add?