October is a great time to go. Crowds are pretty manageable, the weather is usually pretty good, and you have both the Food and Wine Festival and the Halloween Party to enjoy.
But be warned - it can be brutally hot and humid in October. I went in mid-October 2009, and we had record-high heat (low 90s every day and very humid). I've been in October several times, though, and that was the only time the heat was nearly unbearable - most of the time, it's hot but bearable. No way of knowing!
And also be aware that October is hurricane season. I was at WDW in October 2005 for Hurricane Wilma. It ended up being fine -- we got the outer fringes of the storm, but they only shut down the parks for about two-thirds of a day. Realize that even if you don't experience an actual hurricane, you might have some significant rain during your stay.