Once you've filled your boots with DADGAD or double drop D, why not turn your attention to an open tuning that is very popular for clawhammer acoustic guitar, open Gsus4? It is essentially the same as open G tuning, but with the second string raised by a semitone.
So to tune from standard tuning, drop the first, second and sixth strings down a tone and then raise the second string by a semitone. Molly Tuttle uses this tuning for her track Take the Journey.
