For Fred, there are so, so many solos and dances with partners.
I'd say "Sunday Jumps" from ROYAL WEDDING (where he dances with the hat rack and some gym equipment) is probably his wittiest dance.
I also like "Seeing's Believing" from THE BELLE OF NEW YORK and "Bojangles of Harlem" from SWING TIME.
With partners, well, where to start? "This Heart of Mine" from ZIEGFELD FOLLIES, "Dancing in the Dark" from THE BAND WAGON, "Let's Face the Music and Dance" from FOLLOW THE FLEET, and, for a comic number, "How Could You Believe Me" from ROYAL WEDDING.