Some songs I've heard while pumping:
Black Dog, Led Zeppelin
Nights in White Satin, Moody Blues
The Reaper, Blue Oyster Cult
Free Bird, Lynyrd Skynyrd (seriously)
We Will Rock You, Queen
The last one was the most jarring. I mean really.
Today, I finally heard what I deemed an appropriate song for the environment (the chorus, at least) -- Red Rubber Ball by Cyrkle:
And I think it's gonna be all right.
Yeah, the worst is over now,
The morning sun is shining like a Red Rubber Ball.