GCD will get me through Leavin' on a Jet Plane, tookat_ said:With GCD you can play a lot of songs. Off the top of my head just GCD will give you Every Rose Has Its Thorns, Boy Named Sue (capo 3rd fret to match the recording), Ring of Fire, Brown Eyed Girl, The Gambler, Sweet Home Alabama, and I think Wheat Kings. Add an Am7 and you can do Knockin on Heaven's Door, add Bb, F, E and A just briefly for Crazy Little Thing Called Love, add an Em7 for Good Riddance, add Em and Am for Take it Easy. Just G and C are enough for Unknown Legend (Neil Young).
If you want rock/metal stuff then focus more on power chords instead of the open chords to start.