Webshops
Club des Cent Cols sells accurate passlists for the various areas of the Alps and the Pyrenees (see: ‘La Boutique’).
Omni Resources in USA, has very many maps. Perhaps the most interesting section is the Hiking maps of the International section.
Maps Worldwide in UK, has many relevant maps.
Stella Alpina in Florence, Italy is a good place buy maps from (esp. of Italy).
Au Vieux Campeur in France, sells a lot of maps.
Freytag & Berndt in Austria is the best resource for maps of Austria and nearby regions.
French maps could be bought directly from IGN France.
Librera Desnivel in Spain, sells Spanish maps.
Tienda Verde in Spain, also sells Spanish maps.
Denzel-Verlag sells the classic reference book – Grosser Alpenstrassenführer – for travelling on mountainroads in the alps by Motorcycle (but with much relevant information for the bicyclist as well)
Altigraph in France, sells many books on profiles of climbs.
OCD CycloClimbing also sells some guides (but may not be very up-to-date, although work is underway to update them and make them available online), but a recommendation is to get the Roughstuff Cycling in the Alps book by Fred Wright to read about some possible and less possible unpaved crossings in the Alps.
Ediciclo is an Italian publisher of cycling books, many of relevance for cycling in the mountains.
100 Alpenpässe mit dem Rennrad is a book by Rudolf Geser (who has released similar titles for motorcyclists and car drivers).