The Canon LTF 19mm F3.5 FL is difficult to find, but similar to, and 1/3 to 1/2 the price of, the Leitz Super Angulon. I had a nice one until recently, and it was entirely satisfactory for my many uses. Worked great on my Leicas too, and has a lower-contrast "look" to it. If you get the FL model, you will also need the Canon Adapter B to get you to LTM.
I've also owned the 21mm Voigtlander Skopar, and it's contrastier (as one would expect) and sharper as well. A bit too clinical, for my tastes, so I sold it. Was particularly fantastic on the M5, I remember.
"Scientists today announced they have discovered a cure for apathy. Unfortunately, no one seems to care" -George Carlin