Actually, the lowest crowds of the ENTIRE YEAR are in early December--about 4 days after Thanksgiving up until about Dec. 19th, when it starts to pick up again.
The Unofficial Guide to Disney (by Bob Sehlinger) charts attendance each week of the year at Disney, and early December is as low as it gets. We went from the 10th- 15th of Dec this year, and it was fantastic--we walked on to almost every ride at every park, it was great!
And what do you mean by bad weather, Brian???? Sunny and crisp in the low 60's to high 70's--that beats the summer heat and humidity any day--and you also don't get any of the summer afternoon rainshowers. Not to mention you're not battling hot, sweaty crowds--it's a no brainer!