You can purchase discount WDW tickets through AAA, and we have heard that American Airlines offers discount WDW vacation packages. There are not many licensed ticket brokers that will save you a huge chunk of change, and the ones that claim to save you a huge chunk of change are usually illegitimate.
Please beware of purchasing partially used multi-day passes on eBay or on the streets of Orlando (ie: on 192). Disney's ticket readers are patented, and there is no way to prove how many days are left on any multi-day ticket before you purchase it. Disney tickets are also non-transferable and must be used by the same person on all admissions. The new biometric scans help ensure that no one uses your ticket but you.
If you are staying on WDW property, buy your tickets as part of a package. The Magic Your Way ticket structure makes it very worth your while to spend three or more days at the parks. If you come to Central Florida often and hope to spend more than 10 days in one year at the parks, look into Disney's annual passes. Most passes pay for themselves within 6 to 10 visits, and passholders are eligible to receive discounts at resorts throughout the year.