Monday, March 14th, is Pi Day, 3.14. March 14th is also Albert Einstein's birthday! It just doesn't get mathematically better than that!
What is Pi (π)? "Pi is the symbol used in mathematics to represent a constant — the ratio of the circumference of a circle to its diameter — which is approximately 3.14159." Here is a website dedicated solely to Pi (π) - piday.org. This website contains videos and activities you and your class can participate in on Pi Day. Here is a webquest on Pi Day, and here is one more resource from Education World.
An idea that I came up with that students could engage in on Pi Day is having them learn and practice Google Drawings. Here is a simple drawing I made. I inserted a circle shape and labeled the circumference and diameter. Using the special characters, you can also add the π symbol.
I hope these resources are helpful to you, and that you have a fun time participating in Pi Day on Monday!