Demitri has some good points there, and I'd like to add my own.
Sometimes you don't really need misdirection for deck switching, you can do it right under their noses. 'How?' I hear you ask...
Easy. Learn yourself a couple of packet tricks, non-gaffed ones preferably, so they use regular cards from the deck. For example, Elmsley's Twisters Flush uses 10, J, Q, K and A from a suit.
Take these cards from the deck, and then just put the rest of the deck in your pocket, saying something like 'We'll just get the rest of the deck out of the way for the moment.'
After the trick is done, and everyone is stunned with amazement, reach into your pocket where you dumped the deck, and pull out a different deck. Obviously they have to have the same design, but there you have it, a deck switch in full view!
You can also buy Deck Shells here:
http://www.ellusionist.com/order/Deck-Shell.htm
for switching decks.
Hope this helps,