I rarely win anything, but if there is a chance to join a contest, then why not! You never know when it could be your lucky day.
After searching through the weddingsphere, here are some contests that I stumbled upon - hope to find more:
$5,000 Grand Prize from Mirassou Wines - the contest ends on Dec. 1, 2006
Win a honeymoon vacation from Things Remembered valued at $4,400 - contest runs through March, 2007 (they don't give the exact date). And, if you don't win the grand prize, you can still have a chance to win gift certificates - yay.
From Blue Nile, enter to win a Signature Princess-Cut Diamond - their contest ends on November 30, 2006.