Remember last year, when Easter was so early? In 2008, the Vernal Equinox fell on March 20, and the full moon fell right on its heels, on Friday, March 21. The next Sunday after that was Easter, March 23.
You can read it like a treasure map: Start at the Vernal Equinox (which falls on either March 20 or 21 each year), travel onward to the next full moon, and then move to the Sunday after that, and THAT's Easter in a given year.
OK, so we've passed the 2009 Equinox. The US Naval Observatory reports that next full moon comes on April 9, a Thursday. Therefore, Easter Sunday is on April 12, the Sunday right after it.