The easiest way to book rail tickets is through the
Fédération Française de la Randonnée Pédestre (FFRP)
A full list of available topo-guides can be seen and bought from the FFRP boutique.
Institut Géographique National (IGN)
Géoportail is the French equivalent of Google Maps, but with far greater detail. This is very useful when designing your own route.
Map showing all GRs and GRPs
It is surprisingly difficult to find a map on the web that shows all the GRs and GRPs. The only such map that we know of can be downloaded from the FFRP website (it is a big pdf file and can be slow to load).
Alternatively, a hardcopy map with a scale of 1:960,000, which is about
GR-Infos is a useful website for general information about GRs and GRPs.
My long walk
My long walk contains interesting diaries by an American who has walked extensively in Britain, but has also done two long walks in the south of France.