Existing routes:

A cycling highway if you need to quickly cover distance between Aachen and Luxembourg: Vennbahn
A collection of tours in Europe
A collection of transregional (whatever that means?) routes in Nordrhein-Westfalen (Germany)
A collection of local/regional (whatever that means?) in Nordrhein-Westfalen (Germany)
A list of routes in Germany on wikipedia and a list of routes on a German website
In Vosges (France)
Some kml and gpx files of existing routes. Note: river/seaside routes can be boringly flat and busy.

Planning trips:

In Belgium and the Netherlands, for nice routes
In the Netherlands, for fast routes
In Nordrhein-Westfalen (Germany)
In Hamburg
The node system around Aachen in Nordrhein-Westfalen (please let me know if you find an online map of this).
Note 1: Many signs missing/pointing in wrong direction.
Note 2: Cycling routes in Germany can both mean steeper unpaved roads in the woods (for mountainbike) and fast routes alongside busy roads (there is no way to tell by the signs on which you will end up).
Note 3: It seems the little bicycle signs that tell you 'go that direction' (without saying where you will end up) can be both red, square and green, hexagonal for the same route. Do not make my mistake to ignore the green ones.

(I recommend Michelin maps of about 1:200,000 or 1:250,000)

The Wallonian network in the Eifel/Hautes Fagnes (this is also online at fietsnet.be, but map recommended)
For cycling/walking (why both in one map?) in Nordrhein-Westfalen (Germany) (please let me know if you find direct links to 1:150,000 maps)
I found some rarer maps at omnimap
Michelin has no smaller-scale map of Romania. Instead I bought this road atlas although it does contain some fantasy routes and/or unpaved mountain routes.
Note: Careful with river clay in the wet season! Before you know it everything is clogged.
I found this German website but do not know how to use it (instead I use Amazon.de to buy Michelin maps)
Around Aachen and Düren (if you know of larger scale maps please let me know)