Jan de Jong recommended the very professional wandelnet.nl website (in Dutch) for a comprehensive list of hikes 100km or longer. It includes guidebook recommendations.
To translate to English, I used the Babel Fish website. It works quite well, though only one page at a time.
The best part is the interactive map. (screen shot below) On the website version you can hover over the map and click on the routes.
If it ain’t Dutch, it ain’t much. Thanks Jan.
Stichting Wandelplatform-LAW – Lange-Afstandroutes : LAW’s (long routes page)