If you're going to Bruges then hit De Garre, t'Brugs Beertje, Cambrinus, Cafe Rose Red, Vlissinghe, and any other place you see.
In Ghent you must visit t' Velootje. Het Waterhuis aan de Bierkant has cool Singer sewing machine table bases. Dulle Griet didn't thrill me much, but it was years ago.
In Antwerp you need to hit Kulminator, Paters Vaetje, Oud Aersenaal, and Highlander Cafe.