http://www.exploratorium.edu/pi/
I would also share the book Sir Cumference and the Dragon of Pi (A Math Adventure)
by Cindy Neuschwander

For for a deeper look into pi, there is The Joy of Pi by David Blatner.

Or how about Pi Day online greeting cards- http://www.123greetings.com/events/pi_day/
To top off the day, we would celebrate by eating...pie.

image: flickr/djwtwo
So many fun resources online to celebrate Pi Day or my birthday.
(It is also Einstein's birthday, but that's for another post.)