Calculation of date of Easter
Easter (or more accurately, Easter Sunday) has always been calculated as the first Sunday after the first full moon after the Northern Hemisphere's Spring Equinox...
Granted, this can be an absolute bitch to calculate. There are so many different algorithms out there... This function takes a numeric year and provides a string in YYYYMMDD format corresponding to the date that Easter Sunday falls.
This code is also provided in my answer entry under @WallyWest in StackOverflow's Code Golf challenge at http://codegolf.stackexchange.com/a/15644/8555