I don't know if we have discussed this yet, but I would like to know people's opinions on this one.

Why did Gandalf organize the party of 13 to enter the lair of Smaug?

I believe somehow he knew that the ring would be found, or at least had an inspiration in some way that this should be done. Because when you think about it, obviously Gandalf would not do something that would endanger the lives to good folk across the land. Pilfering through Smaug's trove would be certain to invoke his wrath, and indeed who in all middle earth is powerful enough to kill a dragon? I figure he had a premonition that doing this, despite the odds, would be necessary for middle earth.