Since we assume cost is not a problem, then:
If 35mm, then 35mm Summilux ASPH FLE (July 2010 just released).
If 50mm, then 50mm Summilux ASPH.
Both hard to find. Both are the modern, sharpest and most expensive lenses in their class, setting the benchmark by which are lenses are compared. Both got high resale value on secondary market, since people who are sick of being on waiting queue will buy.
Since you are on M9, whether you choose 35mm or 50mm depend on your style of photo. Do you like to be 2 steps closer forwards, or 2 steps further backwards?
Other more "esoteric" lenses depend on taste. I do not recommend those to newbie because you need to have used a number of lenses before you acquire a taste for more esoteric lenses.