You know, I've gotta chime in with all this growl/sing/growl talk. You know the first guy to ever do that [well], was Mike Patton in Faith No More. If you're not really familiar with Faith No More, you probably at least know one song, Epic, which is such a poor example of what the band actually sounds like I've heard some people say they were just trying to rip off the Chili Peppers. At this point I just laugh, because Anthony Kiedis doesn't have 1/4 of Patton's vocal talent, and Epic hit it big a full two years before the Chili Peppers were anything more than a glorified garage band. Not only this, but the rest of their catalog is such the antithesis of Epic, it's hard to listen to the song in restrospect and not feel it was almost supposed to be some sort of joke.
If that's all you've ever heard of them, I implore you to check them out further. They released two really experimental albums in the 90s (that were completely and totally different from each other, by the way), "Angel Dust" and "King for a Day, Fool For a Lifetime." You won't find Epic or any such nonsense on either of these albums, but the music is pure brilliance. They released one more far less experimental album, "Album of the Year" that is also extremely solid before breaking up in 1998. I'd avoid their first three albums right off the bat (We Care a Lot, Introduce Yourself, and The Real Thing) as this is their least accessible stuff; Patton was in his teens, the vocals weren't half as dynamic, and a lot of the music is pretty dated. I eventually got into the early stuff, but not after a long courtship with "Angel Dust" as a teenager. Those last three albums (alongside a few select tracks from the early discs) have been a mainstay of my music rotation for over 15 years (hard to believe it's been that long). Between Angel Dust and King for Day they must cover damn near 20 different genres of music, although there is a recurring "heavy" theme to a lot of it. Having said that, don't write them off if you listen to a track or two and don't dig any of it. Really dig deep; you'll have a hard time believing a lot of it is the same band, not to mention the same singer.
Unfortunately, I'd be hard-pressed to recommend any specific tracks to start with as I'd be afraid I'd pick ones you guys didn't like and it'd ruin the whole first-impression experience, given that they're all so different. I'll just say that "Angel Dust" ranks somewhere in my top 5 best albums of all-time, and I believe each and every track is pure gold. Something interesting on that note, the opening track, "Land of Sunshine," had lyrics written entirely by piecing together fortunes from fortune cookies and catch phrases from self-help infomercials. This probably sounds pretty goofy, but the result is brilliant.
I've strayed a bit here, but my point really was Patton was one of the first (THE first, that I'm aware of) to do the growl/sing switch effectively. His vocal range is incredible. You may have heard him, unknowingly, as he's provided the creature growls and screams to many video games and movies. I know he did all the zombie noises in I Am Legend, for example.