Naturally, the first site mentioned here is the RhB's own website. It is a service-site comparable to those of other railway companies, i.e., you will find the timetable, prices etc., but not much information for the railroad enthusiast or model railroader.
The site that you simply must have seen if you are interested in the RhB is Stefan Dringenberg's “Swiss Narrow Gauge Guide.”
He covers all Swiss narrow gauge systems, but, as our subject is the RhB, this link will bring you to the RhB pages.
Guido Solari Suardi's site Facts and News about the RhB is not fully functional and hasn't been updated for quite a while.
Ralf Holzhäuser maintains an excellent German site, rhbweb.de, where you also find a lot of information about model railroading. Strongly recommended!
A current listing of RhB engines (locomotives, motorcoaches, shunting and Diesel engines) is found on the RailfanEurope site.