.012-.053 use D'addario!! they make great strings. and they sound great for like forever.
NSW Group FTW!

There's nothing incredibly interesting here.
^Really, like, forever? That's so, like, long.
Pfffft, pls stop just blatantly telling people to get this string or that. He already said he's using Dean Markley Blue Steels, or did you not read his post?

TS, those are ok strings, but you should know that no string is going to take kindly to constant changes in tuning. They will fail sooner than later if you do that a lot. Think of bending a paperclip at the same point over and over again, what eventually happens? It snaps right? Same thing with strings. Martins will do it, D'Addario, Dean Markleys.
Ernie Balls might be some of the more forgiving of the list, since they're made more for doing bends and such. They're more stretchy than others I mean.
Have a look at the site I linked to. I haven't played on them, but they might hold up to regular tuning changes.
And as for size, .011's or .012's should be just fine.

I suppose that's why they're called "slinkys," because they can stretch really well. I used to play Ernies on my electric guitars and they always seemed to break more often and not last near as long as the Blue Steels, but I'll definitely look at their acoustic line. Thanks.