The world wide web is full of valuable tools to help you in planning a Walt Disney World Vacation. Here's a list of some of my favorites.
First Trip Planner: http://yourfirstvisit.net/ This is a great site filled with all kinds of practical advice for all things Disney planning.
Trip Booking: The obvious site to book a trip is the Disney World site (http://waltdisneyworld.com). Note: pay attention to the special offers page, located on the Tickets & Packages tab at the top right hand corner (or just click here). This is where you can see the current special deals Disney is offering. For instance, right now, they are offering free dining, $500 gift cards, or room discounts on certain stays.
Learning the ins and outs of "The World":
http://allears.net - Full of information, articles, reviews, and advice on how to make the most of your Disney Vacation.
http://wdwinfo.com - Much like allears, but a little different layout (probably prefer the layout of this site better, but have enjoyed the reviews and advice on allears more.)
http://disboards.com - This is a discussion board on all things Disney. The folks of wdwinfo are the minds behind this one. The beauty of this site is that it's full of information of the people and for the people interested in Walt Disney World. It takes a little time to learn to navigate and get the info you're looking for, but it's chucked full of great thoughts, ideas, etc. You don't have to be a member to view the content. Membership is free, all you have to do is setup a username and password (recommend you don't use your name for your username), and you can post thoughts or questions yourself.
Planning your visit:
http://touringplans.com - I LOVE this site. The freaks (in the complimentary sense of the word) behind this site have done significant research on crowd levels and event offerings. They offer Crowd level predictors for all 365 days. There's an overall crowd level rating, a daily recommendation for best park(s) to visit and park(s) to avoid, and crowd level predictions for each park. They also offer an app for smart phone owners.
Some of the content on this site is free, but the best stuff costs.