Google is celebrating St. George's Day 2013 in the UK with a doodle on its homepage.
The day represents the feast day of Saint George, and is celebrated by Christian churches in several countries, though the doodle appears to be unique to Google's UK site.
Wikipedia provides a little more background on the day:
As Easter often falls close to Saint George's Day, the church celebration of the feast may be moved from 23 April. In England, where it is the National Saint's Day, for 2011 and 2014 the Anglican and Catholic calendars celebrate Saint George's Day on the first Monday after Easter Week (2 May and 28 April, respectively). Similarly, the Eastern Orthodox celebration of the feast moves accordingly to the first Monday after Easter or, as it is sometimes called, to the Monday of Bright Week.
The doodle itself is interesting, showing St. George protecting a princess from a dragon. Here's an oil painting called "Saint George and the Dragon" (via Wikimedia commons) depicting a similar scene: