This seems to be a bit of a growth area, I mentioned Original Snowboard Art recently, additionally Sikko Snowboards offer similar custom skins and Burton have introduced their Series 13 programme that allows you to choose from a range of topsheet designs on a number of their boards, providing that you live in the US (possibly available in Canada too).
I also just noticed that Salomon are running their second annual board design contest with a prize of €2,000 for the winner, closing date is 31 January. If you can cope with the ghastly Flash interface the competition site is here. Via Josh Rubin.