Truca Team have an Arnold shader suite with over 256 shaders available for C4DtoA (using Arnold 5).
There are now two versions of the Arnold User Guides. For example:
If you are not sure which version you are on, have a look at the top and it should say which version, for example: arnold for maya user guide 5
Also, the url for Arnold 5 has an A5 prefix, like so:
John Paul Giancarlo has recorded an Autodesk webinar showing some tips and tricks in Arnold for Maya.
Localisation links for Chinese and Japanese have been added to the following documentation pages:
Romain Chauliac has a tutorial that shows the workflow from Substance Painter to Arnold 5.
Here is an animation test I did using the same technique as these still images, rendered with Arnold.