"20th Century Boy" (T. Rex)

T. Rex and its charismatic frontman Marc Bolan didn't win the kind of fame in the U.S. they did in England, where they literally sparked the entire glam rock genre and inspired millions of teens (guys and girls alike) to cover themselves in makeup and glitter.  The effects of T. Rex wouldn't really be felt here in the States (for better or worse) until the West Coast glam metal wave of the 80s.
In any case, Bolan had a knack for crafting some uncomplicated, gloriously catchy pop-rock.
Bolan (born Marc Feld) started the band Tyrannosaurus Rex as an acoustic folk outfit in the 60s.  He even chose the stage name "Bolan" as an homage to folk-rock king Bob Dylan (and, quite honestly, as a ploy to instantly validate his place in the folk-rock movement).  By 1970, though, Bolan had shifted focus to electric, riff-driven rock & roll that bridged 1950s Chuck Berry with flower child mysticism.  
He painted on some of his wife's eyeliner, shortened the band name to T. Rex to reflect the band's new lean and mean sound, and never looked back.
The non-album single "20th Century Boy" (1973) is one of the rawest, most rocking grooves Bolan ever crafted.  It's anchored by an overdriven, caveman-simple two-chord guitar riff that erupts like a glitter volcano.  And while there's nothing terribly profound in the lyrics—it's mostly a string of similes that equate to an extended come-on to a woman, they sound perfect in Bolan's impish tenor voice.  
The R&B-style backing singers also are a nice touch, giving the track a little nod to funky girl groups, like The Ikettes.  (Incidentally, Bolan would work with Ike & Tina Turner in 1974/5, adding his chunky guitar riffs to the songs "Sexy Ida" and "Baby, Get it On.")