My first Leica rangefinder was the M2 that I happily use today. By the time I got it, I had a number of lenses (mainly LTM mount) to use w/ it; I've sold some of those and purchased others, so I can't say that I got a lense specifically to go w/ the M2 at the time I got it. The lenses that I've most enjoyed using of late w/ the M2 are the Canon 35/1.8, the CV Skopar 50/2.5, and the Canon 50/1.8 (version II, chrome and black).
My first interchangeable lens RF camera was a Canon P, which I still have, and a CV Nokton 50/1.5, which I purchased shortly after buy the P and later sold, mainly b/c I wanted something more compact. The Canon 50/1.5 is my favorite lens for the P.
I've since purchased a couple of Barnack Leicas, but that's another story....