"Suddenly Seymour" isn't a solo. I guess you COULD do it that way. But it's one of my favorite duets...
Also, "Simple Joys of Maidenhood" from Camelot
"Roxie" From Chicago
"Somewhere That's Green" from Little Shop
"Can't Help Lovin Dat Man" from Showboat
"Fine, Fine, Line" from Avenue Q
"That Face" from The Producers is a duet, but I like that one as well
And Millie, "Run, Freedom, Run" is the greatest song. Ever.
"And now for something completely different..."