I know this is an old thread, but I hope this answer will still help someone since no one mentioned here this option so far:
https://github.com/Raruto/leaflet-rotate
It seems to be working pretty well, and it's recently updated. Here's a demo.
As iH8 and many others mentioned, "there is no way of natively rotating a Leaflet map" and there might not be in the near/far future due to this reason.
Meaning that rotating the map using this option will not update the map's labels - so in some scenarios, you might end up with your labels upside-down.