Not a comprehensive list, but understanding these elements (many covered in the Popular Music Harmony documents already posted) can really help understand the use of harmony is wide range of pieces in the jazz, rock, funk, blues, metal and pop idioms. In the future I’ll post some analyses of a range of tunes and show how this wide knowledge is needed to really understand what’s going on in contemporary popular music.
Simple? No. Don’t confuse accessible with simple. To really appreciate the harmony of the Beatles, Beck, Hancock, Gershwin and Stevie Wonder one needs as much understanding as that of ‘classical’ music harmony.