Fretello - Duolingo for learning how to play guitar
ChordIQ - Learn notes, chords, sight reading, perfect pitch and more.
Justin Guitar - Over 750 completely free guitar lessons!
ChordPic - Create beautiful guitar chord diagrams
Uberchord Guitar - Get better on your guitar. Fast.
Hyperlax - Sit back. Relax. Explore faraway places. Enjoy the music.