It's really not my crack (I tend to prefer fantasy and scifi AUs of non-fantasy/scifi shows) so I don't have many, but transference by scuttlebutt inc (two author team) is good: http://www.fanfiction.net/s/4555190/1/Transference (Zukka) as is Irrel's AU, which is a Zutara webcomic http://paolairene.com/irrelsau/?p=157 (though it has not blind!Toph which pisses me off) hmmm, really don't know many. I know a couple of modern technology but not our universe fics too, but it's really as I said, not my crack.