I have now seen many of the Belfries inscribed, 15 I think. Perhaps the most impressive is the Belfry of Onze Lieve Vrowkathedraal in Antwerpen (pictured) which contains four major paintings by Rubens and is well worth a visit, it shares a square with the Stadhuis which is also inscribed. In the rest of Flanders, the one in Mechelen is massive, the one in Brugge seems to be too big for the area it inhabits, Gent has a very interesting one with statues of the former guards on it, and the one in Leuven is odd as it was never completed but is set in a fantastic city with much a more impressive neighbour in the shape of the Stadhuis. I also visited the Cloth-hall in Ypres when I was on a school trip to WWI battle sites, and surprisingly I remember it but not too much of the detail.
In Wallonia the most impressive Belfry was the one at Tournai which is right next to the Cathedral, it has some excellent multi-lingual exhibits inside that explain the role of the Belfries very well, I also managed to catch a look at the one in Mons on the way to the Flint mines at Spiennes.
Of the new ones added in France I have seen many from differing modes of transport and the one that sticks in my head is the one in Lille as it was big enough to make an impression from the Eurostar train. I did manage to stop and get a good look at the one in Calais lit up at night, which was surprisingly nice, as the city, to be polite, is not surprisingly nice!
It is defiantly enjoyable to visit these cities and there is normally much more to see than just the Belfries. In this corner of Western Europe you also have some of its best food and in Belgium especially its best beers to make the experience all the more enjoyable.