I found the SA 21/3.4 to be a pain on the R-D1: metering didn't work (exposure comp wasn't always enough, depending on focus distance); and there was tremendous light fall-off at the sides (again depending on aperture and focus distance).
The CV 21/4 is great, very compact and fast handling.
Ive not tried one myself, but I've heard the Leica 24/2.8 Asph is great. If you like a vintage look, try to find a clean Canon 25/3.5 in LTM. Very compact, lovely lens.
In a 28mm, the Leica 28/2.8 Elmarit-M Asph is superb, compact, a classic street lens. The M-Rokkor 28/2.8 is also special, if you can find a clean one. The CV 28/3.5 is also wonderful, sharp, small, solid. For a vintage look, the Canon 28/2.8 LTM is a classic street lens, though much lower contrast than the more modern lenses.
And, in a 35mm, the UC-Hex is awesome, as is its forefather, the W-Nikkor 35/1.8.
::Ari