Here is a link to a YouTube tutorial that shows you one of the main finger-picking styles that John Mayer uses on his albums. From his recent album
Continuum the songs "Heart of Life" and "Stop This Train" use this technique.
This took me a ton of practice to get it down correctly but since I have learned it I can't stop playing it. And using this technique on many random and boring chord progressions can add a lot of life to your music.
John Mayer finger-pick tutorial