For "normal" focal length, I really enjoy using the 50/2.8 Elmar-M V2; as far as I can tell it's relentlessly sharp and its collapsability makes it extremely compact on any M. On my M8, I use the CV 35/2.5 Color Skopar PII, with the crop factor provides the equivalent of 47mm.
For a wide, it's the CV 15/4.5 Super-Wide Heliar, hands down.