Open A: E-A-C♯-E-A-C♯ or E-A-C♯-E-A-E
Open B: B-F♯-B-F♯-B-D♯ or F♯-B-D♯-F♯-B-D♯
Open D: D-A-D-F♯-A-D
Open G: D-G-D-G-B-D or G-B-D-G-B-D
Open F: C-F-C-F-A-C
Open C: C-G-C-G-C-E
http://en.wikipedia.org/wiki/List_of_guitar_tunings#Open_A
Guitar: Open tunings