Not sure whether I'm still on time but here is some more stuff.
There is a classic car museum on de Cinquantenaire, called Autoworld. Also on the Cinquantenaire is a pretty big military museum showing from shiny knights armor to fighter planes. If you're into that kind of stuff.
If you are into art and stuff go to the Royal museum of fine arts - close to the king's palace in downtown Brussels. There is a part for classic and for contemporary art.
If you are looking for a good restaurant - you may have noticed we know how to eat well in Belgium - try "La Roue d'Or" in the Rue des Chapeliers (just off the Grand Place ... or "Les Brigittines" on the Place de la Chapelle. Neither is cheap but the food is excellent. Don't eat in a resto on the Grand Place or in the Rue des Bouchers. That's for the tourists
To discover the european cartoons go to the "Centre belge de la Bande dessinee" I think it's in the Rue des Sables, walking distance from the royal palace too.
If you wanne see an old medieval castle go to Beersel just south of Brussels. Take the highway E19 in the direction of Paris and get off when you see exit "Beersel". It's indicated. One of the best examples of these old things.
Not sure exactly what you like so I was just shooting some stuff. Let me know what you like I can give you more info.
If you have time available you have to go a day to Bruges. Nothing in Belgium is far, except for belgians themselves cause we are used to everything being small.
Ah, and don't forget to go to Antwerp ... my town
Enjoy the