I second all of these:
"Something Bad" - Wicked
"Send in the Clowns" - A Little Night Music
"Love From A Heart of Gold" - How to Succeed in Business Without Really Trying
"I Should Tell You" - RENT
I fourth (or third) the defense for 1776. The score is just brilliant. But I'll tell you this one thing, my dad is SO against the song "Our Little Secret" from PROMISES, PROMISES. I agree with him, but I only like the last part of the song where it's more upbeat. Other than that, that's my pick for the worst Broadway song ever.
"How could she just suddenly, completely disappear into thin water?" - The Little Mermaid