Actually, there are many guitarists who are best-known as lead players, but whose rhythm guitar work is underrated. Jimi Hendrix, Eddie Van Halen and Stevie Ray Vaughan all come to mind, and I'm sure there are many more.
As far as pure rhythm guitarists go, I'd agree Malcolm Young is one of the best. So was James Hetfield, at least back in the 1980s. And even though he solos occasionally, Dave Mustaine is mostly a superb rhythm guitarist. (I heard Mustaine played all the solos on the new Megadeth album, does anyone know if that's true?)
[!--QuoteBegin-Onhell+Oct 20 2004, 01:04 AM--][div class=\'quotetop\']QUOTE(Onhell @ Oct 20 2004, 01:04 AM)[/div][div class=\'quotemain\'][!--QuoteEBegin--]And thank you for staying on topic [!--emo&

--][img src=\'style_emoticons/[#EMO_DIR#]/cool.gif\' border=\'0\' style=\'vertical-align:middle\' alt=\'cool.gif\' /][!--endemo--] oooohhh yeeeeaaah
[snapback]89599[/snapback]
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Not if I can help it! [!--emo&

--][img src=\'style_emoticons/[#EMO_DIR#]/tongue.gif\' border=\'0\' style=\'vertical-align:middle\' alt=\'tongue.gif\' /][!--endemo--]
Adrian Smith knows the complete works of James Joyce by heart.
Adrian Smith is the secret leader of the Illuminati.
Adrian Smith is legally a sovreign nation.
Adrian Smith has six toes on each foot.
Adrian Smith is so popular that even the Alpha-Draconians love him.