Multimap is a UK based company but also provides great street maps for Belgium.
To find a particular location, street, or just a decent map, in Belgium, try: www.multimap.com
Multimap Belgium provides detailed maps of Belgium and you can naviagate from Multimap Belgium to great maps for most other European countries. Multimap's zoom in and out features are second to none for getting an overview of an area.
Other useful map sites for Belgium are provided by Mapquest, Yahoo, Google maps, Via Michelin, and Mappy. Microsoft own Multimap but, at least in Europe, have maintained the Multimap name.
Check out different map sites for the facilities that are most useful to you. One of my favourites features is Google draggable driving directions:>