M-Rokkor 28/2.8 -- Sharp, contrasty enough, great wide open, smallest M mount 28mm I know of, great build and ergonomics.
Summaron 35/2.8 -- Sharp, great tones in b&w, perfect size, build, ergonomics.
Summicron 50/2 Rigid -- Love it for b&w, smooth as silk mechanics, beautiful retro look to the design.
If I'm allowed to stray into LTM territory then the UC-Hex 35/2, CV 28/3.5 and Nikkor H.C 50/2 might make the list.
Ari