The best-suited for Leica M is probably Novoflex
Miniconnect, which is basically just a little round button that attaches to the tripod socket, little larger than a soft release.
There was an older system called the Q-Top from a company called "ideesign" that was similar, bigger, a bit more solid for big cameras, but that has been sadly discontinued.
The industry standard would be any Arca Swiss-compatible system:
(picture from this site which explains the system, too)
An example of a good Arca Swiss-compatible system are the holders and plates available from
Really Right Stuff. Their separate plates are a fair bit bigger than the Miniconnect though, which makes them work not so well with Leica M. Really Right Stuff also has Leica M baseplates with an Arca Swiss compatible holder built in (it's just the shape of the baseplate), with an optional L-bracket for vertical orientation:
They're expensive at $140 to $200 or so, and rather fiddly; they also have lots of extra little holes for accessories that you have to plug with rubber plugs, about which people have been complaining, while others have been happy.