1. Dress in pi-themed clothing or other items!
2. Bake and eat pies on Pi Day!  Chicken pot pie, shepherd's pie, pizza pie, apple pie...
3. Decorate foods with the pi symbol.  Cakes, cookies...
4. Eat foods with pi in the word.  Pineapples, pizza...
5. Learn about pi here or here or here.
   
6. Write a "Pi-ku!"  Like a haiku, but a pi-ku has 3-1-4 syllables. 
7. Visit the Exploratorium in San Francisco.  They celebrate pi during the school day, but they have events in the afternoon and evening, too!  The exhibits are up through the month of March, as well.
8. Send a pi-greeting card to Grandma.
9. For your afternoon/evening walk, walk pi miles.  (Walk approximately 3.14 miles.)
   
10. Take the Pi Day Challenge.
11. Have a "Memorizing Pi" contest!  There are a million digits of pi in this link, but you can surely manage to memorize a handful of them! Challenge your siblings to memorize the most digits of pi.  The person who memorizes the most digits in 3.14 minutes gets out of clearing the table, washing the dishes, or any other chore of choice!
    
12. Watch the videos below.  Discuss!
    
13. Read the infographic posted below.  There are lots of cool pi facts in this one!  Enjoy!
14. Did you know the U.S. Congress declared March 14, 2009 National Pi Day?  Read the text here!
    

Videos:

Calculating Pi with Real Pies

"Pi and the Size of the Universe"
The next video suggests we can stop at 39 digits of pi to be able to measure the circumference of the (observable) universe and be accurate to the width of a hydrogen atom.  It also includes a brief history of pi at the end.  Perhaps we should use 39 digits of pi instead of the three we usually use in class...?  (And--side note--no decimals in Archimedes' day?  Only fractions?  What a glorious universe! ;) )

Pi and the Size of the Universe

Pi facts:

Visualizing Pi infographic

Any other ideas?  Let me know!