Must sees Flandres:
Near Brussels: Zoniënwoud (a big forest around brussels: tervuren, overijsse,...)
Palais De La Justice (next to the building you have the most beautiful vieuwpoint of brussels).
If you walk back direction Central station from there you will pass some interesting places: Place Sablon, old buildings, palace, Mont Des Arts (another great point),...
If you walk further to the Nord-station (back of central building, you'll pas some other beautiful places). Near Nord Station: Les jardins Botanique, Koning Albert II-laan (with loads of new towers for architecture freaks). From there it's not far from rue Neuve, the most popular shopping street of Brussels. If you just follow that street and cross Place de la Monnaie (Muntplein in Dutch), you're close to Grand Place, La Bourse, Central Station, rue des Bouchers (street full of restaurants),...
Flanders: The coast: Oostende - Nieuwpoort - De Haan - Zeebrugge - Blankenberge - Knokke (Zwin-park)
Cities in Flanders:
Bruges - Damme
Southern part of Belgium is very interesting for hikes & car trips
Viroin-région: Mariembourg - Viroinval (just discover all the small villages in the neighbourghood, go check the viewpoints,...: Vierves-Sur-Viroin, Olloy Sur Viroin, Nismes, Fagnolle, Petigny, Matagne-la-petite, Matagne-la-grande, Dourbes, Roly, Villers-En-Fagne, cross the french border to Givet (beautiful city next to the Meuse river)
Bouillon & Semois river région: Bouillon, Frahan, Rocheaut, Vress-Sur-Semois, Corbion, Curfoz, Poupehan, Botassart, Lafôret ... some further: Chassepierre - Florenville
Durbuy: Bomal-Sur-Ourthe, Wéris, Ny, Mohiville, Barvaux.
You can also do a walk next to the ourthe river from Barvaux to Durbuy centre.
Philippeville - Boussu-Lez-Walcourt - Cerfontaine: an area with beautiful valleys and some of Belgiums biggest lakes: Lac de la Plate Taille (the most impressive one), Lac de Virelles, Lac de Féronval, Lac De L'Eau D'Heure,... you drive from lake to lake ...
Another great cartraject: Floreffe - Namur (visit the city) - Wépion - Profondeville - Annevoie (popular "Gardens of Annevoie") - Salet - Haut-Le-Wastia - Anhée - Evrehailles - Purnode - Spontin - Crupet and at the end of the day go a little back south to Dinant.
another one more eastern: start in Vielsalm - Trois-Ponts - Stavelot - Francorchamps - Malmedy - Waimes- Robertville (lake) - Butgenbach (castle) - Sourbrodt (visit naturepark Hohes Vehn). It's just amazing place.
others: Abbey Of Orval, Abbey of Maredsous, castle of Chimay, Parc Paradisio, Abbey of Villers-La-Ville, La Roche en Ardenne,...
Some belgian beers: Kriek Lindemans (hard to find but very fruity beer, worthwile looking for), Duvel, Vedett, Jupiler, Stella, Chimay, Westmalle, Kasteelbeer, Orval,...
Food: try buying fries! (but only outside Brussels).
Popular discotheques: Fuse Brussels (saturday), La Rocca (Lier - saturdays & sundays)
Radio: Studio Brussels FM 100,6 or 102,1