If you don't know Closer Than Ever, go listen to it now. And watch this clip above of Lea and Joan Almedilla singing "It's Never That Easy/I've Been Here Before" to see why Closer Than Ever is on this list.
Closer Than Ever is a musical revue of some of the greatest music and lyrics written by Maltby and Shire that played Off-Broadway in 1989. There's a four-person cast: two women and two men. There is no dialogue, and every song is self-contained. Many of them are cut songs from their other musicals. (Lyricist Richard Maltby Jr. was actually working on the original production of Miss Saigon in London and Closer Than Ever at the same time.)