There is a place called Belga Queen, http://www.belgaqueen.be/, that my wife and I liked a lot. Not cheap, but great good. The decor was described to me as chic but very late 1990s, and I found that accurate. Still, no complaints.
Another places recommended us by a Belgian friend, for a kind of older "authentic" Belgian place is Aux Armes de Bruxelles, which is kind of in the touristy part of the city and has stained glass, etc. outside. I kind of wish it hadn't been closed when we were there: http://www.auxarmesdebruxelles.be/.