My favorite time to go, especially early-to-mid May. The crowds are moderate and the weather is beautiful - low humidity, warm but not too hot. It is not totally dead like September - there are just enough people to give the parks a festive atmosphere but the lines are not too long at all. Before my oldest DD got to middle school, May was our first choice for visiting WDW; those were the days! Now we go during Spring Break - still fun but I do long for those May trips!