Wicked is the title of the book from which the show was adapted. Not very innovative.
I find that the most special titles tend to be those that are some form of a metaphor for the show's theme--titles you can't fully understand until you've actually seen the show.
I know the thread asks for the best title of a "musical", but two thoughtful titles of plays that come to mind in this respect are
The Retreat From Moscow and
Rabbit Hole.
"Winning a Tony this year is like winning Best Attendance in third grade: no one will care but the winner and their mom."
-Kad
"I have also met him in person, and I find him to be quite funny actually. Arrogant and often misinformed, but still funny."
-bjh2114 (on Michael Riedel)