ChordIQ - Learn notes, chords, sight reading, perfect pitch and more.
ChordU - Extracts chords from any song, integrated YouTube.
7Pad Scales and chords - Music instrument and assistant for playing scales and chords.
Chordify - Chordify turns any music or song (YouTube, Deezer, SoundCloud, MP3) into chords.
Simply Piano - Fast and fun way to learn piano
Riffstation - The web version is Free and you can learn how to play Chords with Youtube Songs.