A few that I like:
Hex - the video is slightly over-long, especially for repeat visits, but the whole preshow areas/music etc set the tone really well.
TOT Tokyo - I don't actually like the other three; they're basically just a video. Tokyo's is excellent though, with the whole "window" effect and disappearing idol.
Mystic Manor - Mostly for the amazing animatronic and the line, "Ooohhhhh yeeeesssss, you like that box, don't you?!"
A few others popped into my head, but I'd put them more under "Queue Line" than preshow, so I'll leave it there for now.