Two from us: We are not being immodest. They do offer a lot of information about cycling in Alsace, Germany, the Netherlands and Switzerland.
If you need to take a train with your bike then our contribution to the AtoB website (http://www.atob.org.uk/bike-rail/bikeeurope-germany/) could be of interest.
www.bicyclegermany.com Maxa and Tim Burley's website with the distilled wisdom of over a decade's cycling in the Fatherland.
www.cycletourer.co.uk/cycletouring/germany.shtml An excellent review of cycling facilities in Germany.
http://www.germany.travel/en/leisure-and-recreation/cycling/cycling.html The German National Tourist
Office's website has extensive descriptions of the major signposted cycling routes in Germany.
http://www.radroutenplaner.nrw.de/RRP_home_02_en.html lets you plan cycle routes in North Rhine Westphalia.
http://www.radwanderland.de/cgi-bin/cms?_SID=df9edb615996e8707829748c76bdfc1dee426a4a00140470070523&_bereich=ansicht&_aktion=detail&schluessel=radwanderland&_sprache=en lets you plan cycle routes in Rhineland Palatinate, not only in its wine country.
We mentioned the joys of cycling in Saarland recently on this blog: http://europeancycling.blogspot.de/2012/03/saarland.html#comments.
http://www.radroutenplaner.hessen.de/rphEN/rph_index_01.asp?Inhalt=rph_home_01.html lets you plan cycle routes in Hesse.
http://www.niedersachsen-tourism.de/en/aktiv-vital/rad-fahren/tipps-highlights/index.php offers information about cycling in Lower Saxony.
http://www.sh-tourismus.de/en/cycling-in-schleswig-holstein offers info about cycling in the North of Germany and into Denmark.
http://www.m-vp.de/english/8026.htm gives details of tours in NE Germany.
http://en.wikiloc.com/trails/cycling/germany/sachsen offers info about cycling in Saxony.
Unfortunately the tourist authorities of the province of Saxony Anhalt are of the opinion that only Germany speakers are interested in cycling there: http://www.sachsen-anhalt-tourismus.de/xxl/de/829429/index.html .
We just returned from a week in Thuringia and can heartily recommend it. There is some information under to be found http://www.thuringia-tourism.com/travel-hotel-holiday-tour/radweg-thueringer-staedtekette-105795.html.
http://www.saxonytourism.com/go-active offers information about cycling in the province of Saxony.
The Brandenburg Tourist Office's website (http://www.brandenburg-tourism.com/pages/cycling.html) offers a compact description of the major cycle tourist routes in the province.
Berlin offers a lot to the cyclist: http://www.guardian.co.uk/travel/interactive/2011/aug/19/cyclingholidays-berlin-routes-maps-socialist-architecture-war-potsdam?INTCMP=ILCNETTXT3487 and http://www.guardian.co.uk/environment/green-living-blog/2010/apr/22/bike-blog-cycling-berlin.
Bavaria is not only a very big province, it offers a wide range of cycle routes: http://www.crazyguyonabike.com/doc/?o=1&doc_id=2876&v=NV.