Ended up getting a iiif, I think I want a normal 50mm for it. Something like a canon 50/1.8 maybe? I thought about the 1.4 but it seems big and will block the viewfinder. Or if you have a summar or summitar I will consider that too.
I've got a very nice 50mm f2 Nikkor lens in LTM for sale in the classifieds here.
If you aren't interested in that, I can recommend the Canon 50mm f1.8. I have one of those and I love it. I tried a 50mm f1.4 Canon a while back and it was not as sharp as the f1.8 canon. The Nikkor I'm selling is very sharp, too and so is the Summitar (I have one of those, too!).
Be wary a lot of the Canons have hazy inner elements. Still plenty of good ones at reasonable prices.
Also consider the Elmar , nice and compact, classic match for the Leica.
Both a prone to lens flare, handy to get a hood as well.
Industar 52mm 61L, from the FSU is a great little lens, when CLAed, which many do themselves with online instructions.
One of these would allow you to save a few bucks back for a more desirable lens or a good 28 like the all metal, silver Solor Skopar, as a 'normal' carry lens.
Also, the FSU FED? turret viewfinder is a good value, covering up to 135mm lens settings.