See, you either love Claudio's strange voice, or hate it. I'm in the former, but I can understand why people are in the latter. In the context of the thread, their bass player does the little bit of screaming that they incorporate, and he's got some good lung burners in there.
I'll stop my Coheed thread derail after this explanation for why I love that particular band, and why I'm surprised more chewers aren't into them. Musically, they're a conglomeration of Pink Floyd, Rush, and Zeppelin, with a modern aggressiveness. Lyrically, their songs all follow a sci-fi comic book that the lead singer is putting out at the same time. Claudio's voice, while sometimes quirky and strange in the highest registers, can still deliver some great sounds too. Anyway, I have no idea why anyone would compare them to The Mars Volta. Two completely different animals.
To add in another great screamer, Joan Jett has some great ones in there.