Any of the Leica 5cm 2.0s (Summar, Summitar, Summicron, in order of decreasing age and increasing technical "quality"), plus a variety of lenses by other makers, the Canon Serenar f/1.8 included. My personal favorite is the Summar, as it looks the most unique by far. With the other ones, I really do not see a breathtaking difference from my Canon FD 50mm, Pentax 50mm, or Nikkor 50mm lenses...except that these SLR lenses do not flare as badly. The difference is there; is is just not huge like with the Summar. All Summars were uncoated, to my knowledge, and I love the way they "fog" the shadows (not really; they are just low contrast lenses), and the way they render the out of focus areas. I wish there was an SLR lens that created this look exactly. IMO, all the "problems" with this lens that the later models improved upon are really what make the lens so wonderful.