As a football fan, the biggest for me was Jamie Carragher outside his sports bar in Liverpool but probably the most famous worldwide would be Zack Efron.
Ruined a holiday for Sarah Jessica Parker a few years ago. And her husband Inspector Gadget/Cable Guy actor Matthew Broderick. Met Dimitar Berbatov and Martin Petrov on work experience a few years ago too.
On holiday in Mauritius a few years ago, Charlie Simpson formerly of Busted, currently of Fightstar i think...was staying at the same hotel as me. Sad thing is, he wore a beanie hat and sunglasses the whole time even though it was 27 degrees to try and hide his massive celebrity status....