Bad Religion's a good one, but Greg Graffin doesn't make music as a skeptic, if that makes sense. It seems more like he writes his tunes, and happens to be a skeptic—ie, skepticism isn't the focus. (Just to clarify my position above.)
Greg Graffin definitely fits with the OP, though.
Boy, I don't know....I think GG absolutely writes music AS a skeptic.
A full-blown realist
And I guess I'm full of doubt
So I'm prone to hear you out and refuse
There ain't no fear in this
It's for all to see, so don't talk of hidden mysteries with me
One of many songs of the same vein.....
AQ: Nearly derped out with Randi myself. Luckily it was at a Capitol Area Skeptics fundraiser breakfast, and he wandered from table to table....so we got to chit chat, get books signed, and he even did some slight of hand with the salt and pepper shakers.... Best. Breakfast. Ever.