Pretty much any of the pieces of shit that autotune the fuck out of their voice in any given song today. That song by Hoobastank a few years back just infuriates me because of it. Chad Kroeger would be up there for me as well.
Actually, I think it might be James Hetfield. I wish they'd just do instrumentals from now on.
It takes some getting used to, but Geddy's voice is fine, and Lemmy's is perfect for Motorhead. Give me a voice with some character over any of the "I can't sing for shit, so I'll just have the computer do half the song" people out there today.
The guy from Green Day has an odd voice that I used to not like as well (doesn't bother me now though).