Here`s the best way to shuffle a pack of cards - with a little help from some maths
(PHYSorg.com Mathematics)

Shuffling a pack of cards isn`t as easy as you think, not if you want to truly randomise the cards. Most people will give a pack a few shuffles with the overhand or riffle methods (where the pack is split and the two halves are interweaved). But research has shown this isn`t enough to produce a sufficiently random order to make sure the card game being played is completely fair and to prevent people cheating.