I can tell you that at MK they do a cute show at the entrance just before the park opens. There are singers and dancers that welcome you for the day, and the train pulls into the station above the entrance. Mickey and other characters hop out and join in. A family that was chosen at an earlier date rides in with them and throws pixie dust to officially get the magic started. I've only seen it once - during my last trip. DH is not an early-riser, but he was willing to get up that morning for some reason. We both loved the show so much that I think I might be able to get him up to go again this year!
I know that there are entertainers before the rope drop at EPCOT, but I think they change from year to year. Last time I was there for the rope drop it was a group of guys who played trash cans ala STOMP. And I think that at Animal Kingdom the characters are outside to greet you as you enter. I could be wrong about that one.