This year's (2008) Google April Fool is a 'Wakeup Kit' as a new feature to their Calendar. Check it out @ http://www.google.com/googlecalendar/new_wakeup.html

Google has previously also did April Fool jokes like the Pigeon Rank, Job Opportunities at Moon, Google Romance, Google Paper Program, Google TiSP (Toilet Internet Service Provider), etc.

Keep exploring & sharing!