Fritland at the Bourse is some of the better but by far not the best frites - experiement with the sauces, the spicy and mayo combined are really good. Each will cost a few cents though.
Don't eat at Le Roi D'Espagne - it could be thought edible but as recent as this past weekend - trapped by a thuderstorm my wife and I gave it a go while waiting to go home and found it average at best.
Chez Patrick across the Grand Place is far better and Cave du Roy is also. El Greco near Le Roi is good but can be a touch hit/miss for some.
Le Roi however as suggested is a great place to have a beer especially for those who like to people watch and enjoy beers but are not beer snobs. Beer snobs need to stop by Delerium - Impasse de la Fidélité 4; 1000 (Post Code) Bruxelles, Belgique - ph +32 (0)2 514 44 34. A spot not too far away and well worth it.
further afield but still quite close to Grand Place for both food and beer - often combined here actually - give In the Spider's Head a try.
In t'Spinnekopke at Place du Jardin aux Fleurs 1, 1000 Bruxelles, België - 02 511 86 95 is pretty traditional stuff and again depending on your taste this will be a smash or a failure. Worth a try to see what the non-touristy stuff is like though.
For good waffels in the area of Grand Place, there's a stand just by Manniken Pis that's very good overall though the best we've had by far in our time living here are to be had at the Stokkel Market - best days are Friday or Saturday but Tuesday isn't bad either. Also by MP is a beer shop that's also got good selection and when not raining, good outdoor seating.
Can't say what is not to miss but I suspect Noord Zee will provide a treat, as would Brasserie Georges (although it's out of the way), and Lola in the Grand Sablon had a pretty upscale Filet Americain, although I've found that many places do it well. I'm also going to recommend the brasserie in the Musee des beaux arts because the space is lovely, the food was good when I went, and the foods are also based on traditional Belgian dishes.
For smaller things:
The frites place right next the Bourse is good.
Au Suisse offers sandwiches and has been there for decades, making it a place to check out. (They did a decent crevettes grises sandwich the last time I was there.)
I wonder if I shouldn't suggest Le Roi d'Espagne in the Grand Place for one place to drink. It's fun and if you're staying centrally that might be a good choice. Meanwhile, I'm blanking on the names of places I've gone when downtown, but usually because I'm passing time before I go to the cinema...
ETA: I've written some things in French, but don't feel obligated to speak it. In fact, probably the opposite: If you don't know Flemish, stick with English as Brussels is in Flanders, after all.
I second Noord Zee. The quality to price ratio is very good, especially for Brussels. For 6 euro, you get freshly cooked fish (you must tell the staff behind the connecting fish shop which fish you want grilled) with salad and bread. Wine is also available. It's not 'restauranty' though. It's like sitting at the bar...outdoors.
I am belgian, I live in Brussels and am not so happy when saying that Brussels is in Flanders. It is a region in itself and is bilingual. (Am not going to start explaining belgian politics now, too complicated). Most people living in Brussels are french speaking (80% of the population).
I am sad you all think that you don't eat well in Brussels. Almost all the adresses mentionned on this thread are on the touristy area. It's like in a lot of big cities if you stick to the retsaurant for tourist the food will be crap and expensive.
I'vread suggestions for les Brasseries Georges that's more in line with what we eat in Belgium than Spinekopke. For a filet americain the best is le vieux saint martin.
The best frites are on place jourdan chez antoine. You can buy your fries and accompany it with drinks in one of the cafe on the place jourdan.
For more upscale restaurant, I would recommand le dyptique à la villa lorraine.
Yes, apologies. Brussels is its own region; I meant to say that Brussels is the capital city of Flanders (whereas Namur is the capital city of Wallonie). And yes, 80% french speaking as you say, but still...politics are complicated and I was unclear. And not like I am one to speak-- my nederlands is terrible... probably saying all this out of guilt.
I was in Brussels for five days and had mostly unmemorable, overpriced food, despite doing my research. We managed to find a couple gems, however, and I'm happy to share them with you:
-For a fun Belgian bistro setting, with good moderately-priced food, head to Fin de Siecle (Avenue Louise 423). We really enjoyed our shrimp brochette with herbed butter on rice pilaf with salad and entree salad topped with giant calamari rings. Maybe not the best bistro food I've ever had, but definitely the best I had in Belgium. Also popular and great looking were the mashed potatoes with grilled sausages, the steak frites, and the carbonnade. No reservations; just show up. Bonus: some of the staff are native English speakers.
-Fantastic hand-pulled noodles and Chinese noodle soups at Au Bon Bol (Paul Devauxstraat 9, near Borse). The spicy beef noodle soup and stir-fried garlicky calamari dish were excellent. And just my 2 cents, but, no, Leffe Blonde does not pair well with Chinese food!
-A little further down the block is Hong Kong Delight (I know, I know, but Chinese is one of the few affordable cuisines in Brussels) at Rue Sainte-Catherine 35. Great steamed ribs and the best "lacquered" duck I have EVER had. I am not a duck lover, and this one, seasoned with 5 spice powder, was fabulous. Avoid the calamari though, it was a bit chewy and possibly from frozen.
-Good frites and sauces (and there are a lot of bad fries sold in Brussels) at Corte Patrick et Fils (on Plac St. Catherine). Look for the pink carnival trailer with lots of lights on the square.
-Fantastic Belgian beers, including some delicious rare ones, at Moeder Lambic (Place Fontainas 8). Spring for the cheese and sausage platter, which is delicious and the perfect thing to enjoy sipping beer on the sunny terrace. The menu lists beers type (blonde bitter, blonde sweet, dark bitter, etc.), and the staff are very knowledgeable about their offerings.
-Fantastic ice cream/sorbets at Tradi Natura (Boulevard Anspach 57). Get the mint chip, peach, or strawberry. Even the cones are delicious. Word of warning: avoid the violet unless you really know what you're getting yourself into (think: edible perfume)
-I also had a very nice meal at the higher-end Les Brigittines (Place de la Chapelle 5). They handled our group of 25 or 30 people very well. We had a set menu of white asparagus with hollandaise, smoked salmon, and a poached egg to start., then grilled steak with mashed potatoes and broccoli, and chocolate mousse cake for dessert. The prices on the regular menu are more than I would normally spend for a meal, but luckily, this was on someone else's tab. Great Alsatian wine, too.
-Monk (Rue Ste Catherine 42) is a nice bar for local nightlife. They have some respectable beers on tap, and it's a fun atmosphere. A little smoky though.
-For a good waffle, insist on one of the freshly-made ones sold from the yellow vans in the museum district by the royal palace. Don't eat any waffles that aren't made right in front of you. That is not something to try after it has been sitting.