Oh good god yes does Billy Corgan drive me mad.
Also, Morissey. And Kasey Chambers - perhaps she is a great songwriter as everybody says, but her voice is so girly and annoying! Finally, one for the Aussies: the bloke from Died Pretty. It's not so much that his voice was bad, per se, it's just that it was kind of toneless. There was nothing interesting about it.
For the record, I like the guy from Clap Your Hands Say Yeah's voice, although I know it's not for everybody. Instead of trying to make out what he's singing, try treating the vocals as just another one of the band's instruments. I find it works pretty well that way.