As most beekeepers have come to realize, particularly in northern climates, wintering bees properly is of critical importance. As with many topics related to the best approaches, there are varying thoughts on how best to to prepare your hive to successfully survive the winter elements. To that end, below are a number of resources you may find helpful. (Note: Some suggestions may be location dependent)
Winter Management from Bee Culture Magazine
The Fall Four by Sassafras Bee Farm
Preparing Beehives for Winter Involves Several Critical Steps by Beekeeper Charlotte
How to prepare your hives for winter: a checklist by Honey Bee Suite
Preparing Beehives for Winter by Eric at Gardenfork
Wintering by Michael Bush (Author of "The Practical Beekeeper: Beekeeping Naturally"