[good old days]

..."I Won't Send Roses" from "Mack and Mabel."

I thought of this one, too! I would also go with "Night and Day" and "If I Loved You."

[TBP]

A few that people came up with in the 2006 list that are favorites of mine:

"What I Did for Love" (A Chorus Line)
"Yours, Yours, Yours" (1776)
"Send in the Clowns" (A Little Night Music)
"All I Ask of You" (The Phantom of the Opera)
"The Party's Over" (Bells Are Ringing)

And from the 2005 list:

"In a Most Unusual Way" (Nine)
"Fallin'" (They're Playing Our Song)