The Virtual Alps is probably the best place on the Internet to start for getting inspiration and ideas of where to go oneself!
Club des Cent Cols again have a wealth of online free information. Their map overlays for France and Switzerland are especially valuable for pass collectors (see the ‘Calques’ section.) To gain real value of the overlays you do well to buy releavant pass guides in their boutique! They also have other interesting information on special passes and some photos. They have a good mailing-list (French).
Our third organisation BIG has a lot of information online of the climbs included in their 1000 climb list. If you become a member there, you will have access to even more information! They also have a forum.
Passi e salite d’Europa has a lot of information on many climbs not accounted for elsewhere with personal descriptions by the author. It covers mostly the Italian and French Alps. (Italian language)
A “commercial/community” style site, in the German language, is Quäldich.de, which is based on good written accounts by contributors. It is especially good for information on climbs in German speaking parts of the Alps. (German language)
Another similar (Dutch, English language) site is CyclingCols.com .
Edwin Seldenthuis’ site Pass a Pass has a lot of (exclusive) information on passes with his own profiles of climbs. (This does not always seem to work, but some information is still possible to find.) (Dutch, but mostly English language)
OCD Cycloclimbing (from where I borrowed the name for this site) have been trying to set up very informative pass guides online and so far made the guide for the Western Pyrenees available (“public beta”). See also their link sections for much important additional information on passes all around. Do not miss Fred Wright’s Alpine Roughstuff page – perhaps the most memorable photos on the web!
An Italian cycloclimbing organisation Unione Internazionale Cicloscalatori (UCI) has some information and many photos of interesting passes on their web page.
Challenging Road Climbs by Roy Ellefsen. – I decided to save these lists for the world as they look abandoned and might get lost. They have served as much inspiration to me and most people interested in climbing really steep roads: Version one (with some descriptions) and Version two (with more climbs, but no descriptions).
(Original versions can still be found: version one and version two.)
Club des Cent Cols has an interesting document on how to calculate steepness (there are others) with some rankings.
Salite.ch & Zani Bike (profile database of over 10000 climbs). The rankings are not always very accurately reflective of the actual difficulty of the climbs, but they could anyway serve to give ideas of challenging climbs. (See also the other profiles database sites on the Profiles of climbs links page.)
Personal web sites of special interest
Marc Liaudon has maps of pass locations in France, Spain, Switzerland and the US plus a wealth of other interesting information.
Gerd Balser has information on more passes than (more than 500) on this site (currently) and a lot of photos/videos. (German)
André Rudaz has information on many interesting passes in Switzerland and elsewhere. (French, Italian)
Patrick Schleppi has a very fine and updated website in several languages.
José Bruffaerts has lots of information on many climbs in the Alps and elsewhere. See the ‘Menu’. (French)
Jean Philippe Battu has interesting information on climbs in France (around Grenoble).
Mario Labelle gave me much inspiration when I started out on my early adventures in the Alps (somewhat old pages now).
Gîtes de France official page for this popular lodging alternative for cyclists and walkers in the French mountains.
Montagna Piemonte has links to the official pages for every administrative region of Piemonte and many of those pages have lists of lodgings in their area. (Italian)
Valle d’Aosta has listings of accomodations in the Aosta valley.
Club Alpino Italiano could be searched for mountain huts and other lodging in Italy.
Südtirol is THE site to visit for finding relevant lodging in the Dolomites and nearby.
Mountain huts around the Alps
Zani Bike has much information on climbs in Valle Camonica and Valtellina in Italy. There is also good information on great climbs like Passo di Baremone and Passo San Marco.
Forum dello Scalatore is a discussion forum for bicycle climbs. (Italian)
Cycling Challenge is a personal website with ever more fine descriptions of climbs mostly in France.
Roobsta.com with information on climbs in the Alps and the Pyrenées.
Die schönsten Paßstrassen Europas and Die Alpentourer are two of several motorcycling pages on passes in the Alps that has many photos. (German, of course ;-))
Biken im Oberwallis is an interesting website with descriptions of routes mostly for MTB in Wallis. (German)
If you are looking into climbing some gravel roads, it might be well to look into a site like Mountain Bike in Piemonte or Liguriabike.it
Mountainbike site for the Imperia and Alpes-Maritimes regions (Ligurian Alps).
The classic resource Trento Bike Pages still has one of the most extensive archives of travelogues and cycling information from all around, but also very much on the Alps and the Pyrenees.
Bicycles on trains in Europe – written for Brittish train travellers, but gives a good idea of how this works in most of Europe. (On regional trains, try and find a place where your bicycle will not be an obstacle to passage (sometimes you are supposed to be in first (or perhaps last) wagon).)