I always wait to ride Monster's Inc. until nighttime. For some reason taht ride is always a walk on then, but has mild lines during the day. I think because it is in an obscure little corner of the park where there isn't much else to do or see. It is one of my faves.
Lines you should expect to be long: Space Mtn, Splash Mtn (if open during your trip), Indy, Peter Pan, TOT, Soarin and Cali Screamin.