The late, great, gone-too-soon one and only Burl Strevel from the Blue Ridge Quartet–with that incredible bass voice from vocal chords that had spent years marinating in cigarettes and whiskey.
Also Tim Riley from Gold City hits some low notes.
Peter Murphy, solo artist and lead singer of Bauhaus. Some of his stuff got ridiculously low.
Winona Judd has a deep voice. She did an acoustic set and I couldn’t believe her range.
Tim Foust from Home Free. He goes LOOOOOOOOOOOOOOOWWWWWWWWWWWWWWWW
Odetta.
Derek Smalls?
Just not a lot of low voices in rock music for the same reason all the big female stars are screechers: The demand is for high voices.
You have to go to other genres to get basses. Yes, this is a bit of a hijack, but how often do we talk about bass singers?
Richard Sterban. And man, ain’t no question.
NOBODY sang as low as JD Sumner.
Except perhaps for Thurl Ravenscroft:
Yes, you have heard that voice before. (Tony the Tiger, The Grinch)
This is just for fun … on all sides.
In jazz, it was Billy Eckstine, Mr. X! When it wasn't Herb Jeffries (who also made cowboy movies, Google "The Bronze Buckaroo"!) And finally, my personal favorite, Johnny Hartman:
The bearded guy in the Oak Ridge Boys is William Golden.
He’s listed as a baritone but sure sounds like a bass singer to me. He goes way do there.
The Oak Ridge Boys were all clean cut guys except for Golden. He sure stood out.
https://pbs.twimg.com/profile_images/954053272427552768/2-_FzzCq.jpg
Peter steele type o negative!
Who was the cat that sang with Olivia Newton John?
Heh. We found the same video.
And Snoopy, Come Home.
I’m officially disappointed in the Dope if I’m the first one after >50 posts to mention Mark Lanegan.
ETA: Wait, I guess I don’t have the ears or music-geekness to distinguish baritone and bass, but dude’s got a seriously deep voice, is what I’m saying.
High voices proliferate in rock because they can be heard over the band. Rock instruments are louder than in country and other genres, and generally occupy spectrum in the mid range and below. So singers like Robert Plant or Steve Perry complement the rock sound nicely. Johnny Cash or Barry White would sound muddy.
If you want to make a country cover of a rock song, turn down the band, add an acoustic rhythm guitar, get a singer with a deep voice and a drawl, and you got a cross-over hit:* “Ah cain’t GAIT no, sat-ees-FAC-shun”.*
Thurl ravencroft…Mr Grinch.
Mick Jagger could get pretty low, e.g. in “She Smiled Sweetly,” a gem from
Between the Buttons (recorded late ‘66).
If we are extending to baritones, I would suggest Waylon Jennings and in rock, Jim Morrison, Robbie Robertson, Warren Zevon, Lou Reed.
For bass singers, all I got is Billy Gibbons from ZZ Top.
Till Lindemann of Rammstein.
Some say he’s a true bass. Others say he’s really more of a low baritone. I say I don’t care! 
Rammstein - Sonne (Official Video) - YouTube (Sonne - Mostly safe for work)
http://www.dailymotion.com/video/x2ruwem (Kokain - my favorite. This is the best quality sound I could find right now)
One thing I like about German bands is that the male vocalists tend to have voices on the lower side. A couple of (non-bass) examples from bands that are very popular in Germany, but not in the United States:
Die Ärzte "Lied vom Scheitern" - YouTube (Die Ärzte “Lied vom Scheitern”)
Oomph! - Augen auf (Video-Clip) - YouTube (Oomph! “Augen Auf”)
Turley Richards had a 5-octave range (lowest at 2:57 here), but it’s more the passion he brought to a song than the “special effects” of his range.
I find that when someone says “Can you believe how low/high they can sing?”, it usually means I’ll be unimpressed by the music (I mean, imagine Thurl Ravencroft duetting with Minnie Ripperton… not much fun).
Have we all lost that lovin’ feeling for Long John Baldry and the Righteous Brothers? Maybe the Rightouses aren’t strict basses, but LJB is pretty close.
Does Boogie Woogie music count?