Tammy,
Planning a trip to WDW with a wide open calendar: priceless!
The basic rule of thumb is that if you can visit WDW when schools are in session you'll likely have lighter crowds. For example, the weeks that follow Labor Day Weekend are times when the park crowds are much lighter, but it can still be quite hot then.
If I could pick a time, I'd opt for the weeks between Thanksgiving and Christmas because I adore the holiday decorations throughout the parks and resorts. It really has an extra dose of magic! You can also opt to attend
Mickey's Very Merry Christmas Party for even more holiday fun.
If you'd like the lighter crowds and more bonus opportunities, September and October are a nice match and have both
Mickey's Not So Scary Halloween Party and
Epcot International Food and Wine Festival.
And finally as long as you avoid MLK Weekend, Presidents Weekend, and the Disney Marathons (1/10/13 - 1/13/13; 2/22/13 - 2/24/13), January and February are also nice times to visit, too.
Happy planning! Please let us know if we can help again.