Sept is a great time to go. The parks are empty because a lot of people don't want to take thier kids out of school when it just started. This year, due to constuction, my school opened Sept 12. So we jumped on the chance to go in Aug into Sept. It was very hot and humid, and it rained almost every afternoon, but the crowds were empty. Every store blasts the A/C, so if you even walk by an open door, you get cooled off. I don't think there are any special events going on at this time.
Oct is nice too. I've never been down there at that time. Mickey's Not So Scary Halloween Party at the Magic Kingdom is going on during this month, which, from what I've heard, is great for adults and kids. I can't tell you more about
MNSSHP, but if you check out allearsnet.com or disneyworld.com or even look around the boards, you find a lot more info.
Nov is another great time to go. It's still warm and nice. I've only gone down during Jersey Week, since I'm off from school then, and it's been busier, but not horrible. There is the Food & Wine Festival at Epcot, which is great for adults. The countries put up stands with wine samples and plenty of food samples, and even more countries set up little booths there. I think the countries change every year, but disneyworld.com should have an annual list that comes out with all the new countries coming in. There is also a great concert series on the stage infront of the American Pavilion. They have various famous singers come and sing a few songs nightly. It's not hugely popular people, mostly oldies or more scarce performers, but it's still enjoyable. Last year Blake Shelton was there, a country singer, which I loved. And my parents watched Eddie Money later in the week.
All 3 times are great times to go. But it also depends on the weeks and holidays. Nov has more busier weeks, with Jersey Week and Thanksgiving, it pulls a lot of people down there. I'm not sure about Oct, but after Labor Day, Sept is pretty much empty.
Good luck with the choosing! And have a magical time when you head down there!!