Double D.

Nah, it's not too late -- just hit EDIT on your initial post and you can also edit the title.

Me, I use DADGAD regularly enough that I keep one guitar in that tuning. On solo gigs, I drag along three guitars: one in standard tuning, a 12-string tuned down a full step in D-standard, and the DADGAD guitar.

@sleigh,

Thought I would leave the title, thought it might get more traffic.

Yes as you already know the difference between DADGAD and Double drop D tuning is only one string, that been the second string from A in DADGAD to B in Double dropped tuning.
But it makes quite a big difference in sound, Double dropped tuning not so modal sounding to my ears.

Like Sleigh I have a guitar that's permanently in DADGAD, and another in open G. DADGAD or open D, I use a lot, maybe even more than standard. Funny, I've been thinking about 'weird' tunings lately. I had some Will Ackerman playing and my wife heard a piece and said, 'can you play this?'. Usually when that happens it's some amazing guitar player and my standard response is, 'ya, I did that on my forth album'. This time I thought I'd give it a try and at least try to find out what the tuning is. Turns out the tuning is, from 6 to 1, F# C# D# A# B D#. Which got me wondering how people come up with these tunings. Is it a modification of a well known tuning or do they just sit there twiddling the knobs until something makes them go, 'that sounds nice'. Will Ackerman has his tunings listed on his website and a lot of them are odd. Must carry dozens of guitars when he's doing a show.