I totally agree about West Side Story. Some of the pure orchestra songs don't sound pretty, but they aren't supposed to like "The Rumble." The harmonizing is so perfect to accomodate what is happening on the stage. Lots of the dance breaks also mesh great with vocals, like in "America" and "Cool." And the slow songs like "Balcony Scene," "Somewhere," "I Feel Pretty" and especially "One Hand, One Heart" combine the orchestra with the voices to make such gorgeous sounds. OHOH in particular has a gorgeous flute/clarinet harmony.
Ooh, also many in Miss Saigon. The instrumental endings of "Last Night of the World," and "I Still Believe" are gorgeous and dramatic, and the instruments play an important part in essentially all the songs.
Other favorites:
A New Argentina-Evita
Memory-Cats
Phantom of the Opera-Phantom of the Opera
Dance of the Robe-Aida
Facade-Jekyll & Hyde
Maybe This Time-Cabaret
Easy As Life-Aida
Stars-Les Miserables
One Day More-Les Miserables
Empty Chairs At Empty Tables-Les Miserables
Rain-Once On This Island
Pray-Once On This Island
Angel of Music-Phantom of the Opera
New Music-Ragtime
Wheels Of A Dream-Ragtime
Fable-Light In The Piazza (La Passegiata as well

)
A Bit Of Earth-The Secret Garden
Actually, most of the songs in The Secret Garden have gorgeous orchestrations.
No One Mourns The Wicked-Wicked
the end of Defying Gravity-Wicked
"If there was a Mount Rushmore for Broadway scores, "West Side Story" would be front and center. It snaps, it crackles it pops! It surges with a roar, its energy and sheer life undiminished by the years" - NYPost reviewer Elisabeth Vincentelli