Recently I picked up a lovely Leica 35mm f3.5 Summaron, and after some quick test shots, I am ready to declare I am a believer. It produces lovely colours and is sharp. Like most rangefinder lenses it won't focus down below 1m, but it is tiny and looks just wonderful on the NEX.
This is my second version of this lens. I also have one in M mount with goggles, which is rather weird when using it on digital.