135 ain't street. You have to be part of the situation to shoot street. It's intimate. Long lenses in public is surveillance (which could be an interesting style in its own right).
If you want to shoot street, get a 50 or a 35.
Summitars are cheap as old chips these days, are plenty sharp stopped down (you want that DoF), have lovely subtle bokeh, weigh almost nothing, and collapse small enough that you can easily shove an M body in your pocket with the lens mounted. I think the Summitar is probably the most versatile value in a Leitz lens. It's fast, it's sharp, it's small, it's light, it's cheap.
Collapsible Elmar is another good option, sharp as a razor and still (I think) the smallest lens you can put on your M. They're slow (3.5), unless you want to pay collector prices for the Elmar-M 2.8.
If price, size, and weight aren't key considerations, get a Summicron. The only bad thing you can really say about a Cron optically is that the bokeh's a little busy, and that's being pretty picky. You can get a collapsible to cut the weight and size to about that of the Summitar. Most (all?) of the collapsible Crons have soft front glass, so you'll pay a premium for a clean one and you'll want to keep a filter on it.
Someone else will have to chime in on which 35s to look for, I've been sticking to 50s while I learn my M.