Well, lets see... for my recommendations:
1) 42nd Street is brilliant I think, as long as you are into dance... it isn't so much of a musical as a collection of different genres of dance, but this is likely the best show I've ever seen in NYC
2) The Boy From Oz was good (I saw it this past weekend), and it stars Hugh Jackman (Wolverine from the Xmen movies) so it has star appeal.
3) Assassins is amazing, it's written by Stephen Sondheim (his most famous work is Into the Woods), and is a comedy about a collection of famous presidential failed and successful assassins. It's good, especially if you know some history.
I'd avoid like the plague any of the overhyped trashy musicals, ala The Cat in the Hat, etc, because they are more gimicky and trendy, not something memerable years down the road.