I have the 90/4 Elmar-C version of the lens Flotsam mentioned. It is truly an excellent lens and relatively inexpensive for a Leitz. It also "kind of" uses the 39mm filters of other Leitz lenses. I say "kind of" because they will fit but not screw in all the way due to a difference in the thread pitch.

The 40mm Leitz and Rokkors are both considered as good as the 35mm Summicrons of the same period. They also are relative bargains.

Another possible wide angle is the 35/2.5 Voigtlander Color Skopar. I have used this lens and can vouch for its capability.