An interesting resource. I've bookmarked that site because it contains a lot of information other than the subject of this thread.
Just thought I'd mention that the Jena Sonnars are worth a look, also. They're not specifically mentioned in the above link, but I know that Zeiss Jena built lenses for Leica sm (dunno about M). From all I've read (haven't yet had the chance to try one out), they're excellent optics. I'm particularly interested in the Zeiss Jena Sonnar 180/2.8 in M42. The folks over at the manual focus lens forum rave about it. Here's a tempting example:
http://cgi.ebay.com/Carl-Zeiss-Jena-...3A1%7C294%3A50