A lot of the more popular rides at the Disney parks have a feature called FastPass. (Universal Studios has these too, but I can't remember what they call theirs.) You put in your ticket and it gives you a time to return to go through a shortened line. These are incredibly valuable for getting through the most popular attractions without wasting three hours of your life waiting in the Florida sun.
Allears.net has a list of which attractions have FastPass lines
here. Most of the rides also have a clock at the front which'll tell you right off the bat how long the wait is, so you can decide whether you really want to wait 2 hrs for Splash Mountain before hand.