I rather like the LTM Leica 50mm Summar f/2. They can be had for about $200 plus the cost of an adapter (avoid cheap ones). The have a LOT of character, and if you are shooting a M9, it is easy enough to add contrast in post processing. I'm also really fond of my Nikkor-S.c. 5cm f/1.4, you can get one with an adapter for under $700, of course part of why I like the one I use is because it was my Grandfathers.
Of course my next lens purchase will be a good modern 50mm f/2 or faster.