"Monkey Man" (The Rolling Stones)

It's funny.  I've been a fan of the song "Monkey Man" from Let It Bleed (1969) for years.  But every time I hear that intro with Bill Wyman's bass and vibraphone, I think that my iPod has shuffled to a song by The Temptations or Marvin Gaye.  It happily fakes me out every damn time.
But from that pseudo-Motown intro, Keith Richards's guitar suddenly snarls with distortion and rips into that unmistakable riff as Charlie Watts's drums smack in you the head from stage right.  It's a raunchy, funky groove from moment one.
"Monkey Man" also is one of my favorite Stones songs lyrically.  The late 60s / early 70s saw Mick Jagger crafting lyrics that were witty, literate, honest, and complex.  On "Monkey Man," he's using blues and drug slang to wryly comment on the public's/media's perception of him and the band, which was that he obviously was a junkie and an STD-ridden womanizer who was constantly bed hopping from one skank to another.  He also addresses the odd dichotomy of fans practically worshipping them and the establishment deriding them as agents of evil, while they themselves were just interested in rocking a little.  (Well, I hope we're not too messianic / Or a trifle too satanic / We love a bit of blues).
In and of itself, all of this would add up to a great song.  But then there's that instrumental bridge that comes out of nowhere and shifts everything into a sunny major key, with Keef's nice slide guitar work and Nicky Hopkins's glorious piano, which somehow borrows as much from honky tonk bordellos as it does from Viennese concert halls.  That bridge just puts the whole tawdry, sack-of-broken-eggs affair into the category of "instant classic."