One of the first things to consider when planning a trip to Walt Disney World is when to visit.  The time of year you choose can have a dramatic effect on the price you pay.  Disney has 5 travel "Seasons" which are (listed from cheapest to most expensive): Value,  Regular, Summer, Peak, and Holiday.  Click here for the 2010 Walt Disney World Seasonal rates Calendar (PDF)

• Value Season as it's name implies is the cheapest and generally least crowded,  this is primarily due to cooler weather and school being in session.   Unfortunately it also means the parks may not be open as late and is when hotel pools, water parks and rides and attractions are more likely to be refurbished. (there are actual multiple value seasons throughout the year in the late summer/early fall and winter.
• Regular Season - Regular rates, not as cheap as the value season but still on the low end of the scale.  Regular season ranges from Late April to early May and then again for most of October and November.
• Summer Season - From late may to early August is the summer season, typically very busy and can be very hot, rates are more expensive and rooms book up early with parents who do not want to take kids out of school in the fall.
• Holiday Season - Maybe the most magical time of the year since Disney really goes all out for Christmas time and the most expensive to boot.  Basically covers the latter half of December starting around a week before Christmas till New years day.  Parks are very crowded, weather is usually cool to sometimes downright cold at night by Florida standards. This season books up very early.

Other Mini-season do exists, typically around holiday weekends and prices will be slightly higher during these times:

• Martin Luther King's Birthday - Jan 15-17th
• President's Day - Feb 12-14th
• Easter/Spring Break Season - March 28- April 11th
• Independence Day - July 2-4th
• Thanksgiving Nov 24-27th
• Week between Christmas and New years - Dec 25-31st

Note: These holiday times are also usually blacked out from any special promotions or deals offered from the Walt Disney Travel Company and are also more crowded than normal. 

Click here for the 2010 Walt Disney World Seasonal rates Calendar (PDF)