After you have learned to play some basic chords, the Ultimate Guitar Chord Chart II is a great chord resource.
It was developed by Phillip J. Facoline, and shows you how to play almost any chord you are likely to need! It is a comprehensive chord chart for the more experienced guitarist with at least some basic knowledge of chords and how to play them. It is a no-nonsense, reference that allows you to look up chord fingerings and positions for virtually any chord. It illustrates over 1200 chord positions using simple chord diagram boxes labeled with the chord name. There are multiple positions / forms shown for many chords.
One handy feature on the Ultimate chart is a listing of chords by key (page 7 of the .pdf file). The following list will give you ideas for developing chord progressions and introducing variations as you write songs and jam:
Chords in the Key of:
Ab or G#: Ab Bbm Cm Db Eb Fm Gdim
A: A Bm Dbm D E Gbm Abdim
Bb or A#: Bb Cm Dm Eb F Gm Adim
B: B Dbm Ebm E Gb Abm Bbdim
C: C Dm Em F G Am Bdim
Db or C#: Db Ebm Fm Gb Ab Bbm Cdim
D: D Em Gbm G A Bm Dbdim
Eb or D#: Eb Fm Gm Ab Bb Cm Ddim
E: E Gbm Abm A B Dbm Ebdim
F: F Gm Am Bb C Dm Edim
Gb or F#: Gb Abm Bbm B Db Ebm Fdim
G: G Am Bm C D Em Gbdim