The Pragmatic Bookshelf is going Kindle and iPhone compatible, with support for .epub (iPhone) and .mobi (Kindle) formats.
I just downloaded RubyCocoa on the Kindle and it looks excellent -- with listings in monospaced font! -- but most of my other books are not yet available in Kindle format.
Pragmatic Programmers have also begun selling tutorial screencasts. I've yet to take a look at any of those, but I think it's a good idea.
Kindle support from Pragmatic Programmers is a big deal. In my mind, PragProg has become the new O'Reilly. Not that O'Reilly has gone the way of the dinosaurs (or, say, Miller Freeman), but Safari access on portable devices is such a huge and obvious plum that the very fact they haven't plucked it makes me think that they must be facing internal issues.