Aside from the fact that three out of the four people you listed are not singers, Beyonce. That woman has some pipes, and an amazonian body. I have a video of her performing on the BET Awards, she danced ontop of her name, onstage, spelled out in 20 foot tall lights. It was pretty damn impressive, and when she was belting it out while dancing and effects were being used to make her voice echo, it was amazing.
"To see the world in a grain of sand, and heaven in a wild flower. Hold infinity in the palm of your hand, and eternity in an hour..." -William Blake
I agree that those choices are not good. They give no variety because just three of them alone are rap. You should have given a choice of "other" at the very least.
In general... TONS of different types of people, etc.
Right now I'm on a Gwen Stefani fix (LOVE the album).
I love No Doubt, Alicia Keys, U2, Jewel, Outkast (depending on the song, but most), Mary J. Blige ("No More Drama" is one of my favorites)... you get the picture.