Just because you have a flat voice doesn't mean you can't be a famous singer!
I thought Lou Reed and Nico were the undisputed champions for flattest voices EVAH, but upon further reflection I think these folks could also enter the contest:
Anthony Kiedis of the Red Hot Chili Peppers
Crash Test Dummies
Death Cab for Cutie
James Hetfield of Metallica
Lemmy Kilmister of Motorhead
Vince Neil of Motley Crue
I am sure some of you will disagree with this list. And perhaps some of you might be able to add some names to it. If so, do tell.
P.S. Full disclosure: I can't sing for shit, and my voice is F-L-A-T. So there. And despite the fact that those listed above have flat voices, I really like one of them (LEMMY!), and can sometimes handle a couple of the others.