I have two lenses in this range that I enjoy using. One is the Canon 19mm F3.5 FL, which I scale-focus, I'm quite used to that. And the 21mm F2.8 Minolta MC Rokkor, which is incredibly sharp, it has a floating-front element. Both of these lenses could be classified as having a cult following. Al Kaplan was a big fan of the Canon 19mm, I remember how excited he was, when I finally found mine. It was worth the wait.
The 21mm Rokkor F2.8 works well on my Nex-3. The 19mm Canon does not fit, due to the internal light baffling.