Dutch:

Auvibel
Bibnet: Flemish public libraries on the Internet:
Flemish Centre for Public Libraries (Vlaams Centrum voor Openbare Bibliotheken (VCOB))
Flemish Association for Libraries, Archives and Documentation (Vlaamse Vereniging voor Bibliotheek, Archief en Documentatiewezen)
Authors Lending Right Work Group (Werkgroep Auteurs voor Leenrecht)

French:

Professional Association of Librarians and Researchers (Association professionnelle des bibliothécaires et documentalistes)
Professional Association of Librarians/Federation of Libraries (Association Professionnelle de Bibliothécaires/Fédération de Bibliothèques (FIBBC))
French Community
the section on public libraries (still under development)
the section of the Francophone Universities (CIUF) website that deals with their libraries
Francophone public libraries
Multimedia libraries in Francophone Belgium

German:

Conventional and multimedia libraries in German-speaking Belgium
List of conventional and multimedia libraries in German-speaking Belgium

English:

International Public Lending Right Association
Federal Public Service Economy: intellectual property, copyright and related rights