one of brussel's hidden gems is a place called "Oki", named after the chef who makes japanese / european fusion food. its on rue lesbroussart which runs between place flagey and avenue louise. not cheap but worth every penny.
for Thai food, Noi is one of the best, located on chausee charleroi, very close to place stephanie
for typical belgian food, stay clear of most places around the grand place (tourist traps). one exception is chez vincent, great for steaks, mussels, waterzooi, etc.