Here's a jazzy little descending chord progression that gets used in lots of songs - from Tito Puentes' "Oye, Como Va" (to introduce a little cross-threading) as done by Santana on the live CD Sacred Fire (where I picked it up) to The Beatles' "Something." Naturally it could be done with any minor chord as the starting chord, but Am seems to be the easiest for illustrative purposes:
Start with an Am barre at the fifth fret: Am - Ammaj7 - Am7 - Am6.
Basically, the only thing changing from chord to chord is the note played on the fourth string - from A at the 7th fret to G#, then G, then F# - a half-step decrease each time. For me, the Am6 fingering is most easily attained by: open A (5th string), index finger barre at the fourth fret across the first four strings, with middle finger barre at the fifth fret across the first three strings.
Play it once and you'll realize you've heard this progression in a countless number of songs.