1)   Chord Miner 1.0.2
Manage chords and chord sets with this superb reference and repertoire tool from the publishers of Guitar and Keyboard Coach. See, hear, print and save the chords you do know, identify the ones you don't, then check out which songs use them.

 2)   ChordSMART 2
An invaluable reference tool for guitar players of any level. ChordSMART shows chords in any key in several tunings, and even shows you optional open strings.