Has to be one of the better ones I've seen today. Here in Australia a radio program strung its listeners along telling them that their GPS units could be tracked by the police and they could work out when you had been speeding. People were on the verge of ripping out their GPS units, untill the show said "April Fools!"
The Australia ABC TV had some egg on there faces when they thought that they had an exclusive interview with David Beckham saying he was switching clubs, untill they found out the guy was a fraud!