If you are going for a week-end I can recommend a visit to La Becasse on a Friday for a glass of Kreik and some bar snacks very small and very friendly when busy you can usually end up sharing a table with others language should be no barrier great fun, before heading to Le Mort Subite for even nicer Kreik and more bar snacks.
Avoid if you can some of the restaurants to east of La Grand Place they are either tourist traps or designed for euro parliament bureaucrats expense accounts some of their prices can hurt!!
Get off the beaten track there are some little gems to eat in.
Saturday jump on a tram by the way it is easier to get a 3 day travel ticket (should only cost about 9�) explore the centre in daylight, go out to Heysel some nice bars out there, take an extended tram ride even the suburbs are equally fascinating with art noveau style houses and gorgeous public parks, visit the flea market in Place Jeu de Balle have a lesiurely breakfast in one of the many cafes around the square.
Sunday go to the market at the Gare Du Midi soak up the atmosphere eat fresh waffles hot from the van washed down with hot chocolate when its cold, take the metro to Clemenceau and visit the most amazing market you will see, the surrounding bars and cafes are great very friendly and welcoming, when you've done that back to Gare Du Midi and track down a bar called La Laboureur the decor is frozen about 1953.
Find a good bar and there are many some well hidden some not after all if you are in Belgium you can only be there for the beer, have a good trip