Progression Free - Guitar TAB Editor for iPad
Damn, this is a really cool app. I've got it on my Mac, but this actually seems to make a lot more sense for doing tab entry; the touch interface really lends itself well to this sort of thing. The samples are decent (enough to get the point across), and the files (.notion) will presumably open in the their desktop version, so you can export to PDF, MIDI, etc. Very cool. And it's free!
EDIT Damnit, on meant Progression on iPad!