5906--9mm, stainless frame/slide
5903--9mm, alloy frame/stainless slide
5904--9mm, alloy frame, 'blued' slide
All of the above are DA/SA.
There's the DAO variants too:
5946--9mm, stainless frame/slide
5943--9mm, alloy frame/stainless slide
I have a 5904 and the curved backstrap fits my hand very well. Gun is accurate and 100% reliable too.