Budget
The matter over which establishment serves up the best frites (locally known as fritkots) remains a matter of heated debate. Some argue that the best frites in Brussels are served at the fritkot near the Barriere de Saint-Gilles, while others defend St-Josse's Martin (Place Saint-Josse/Sint-Joostplein) as the prime purveyor of the authentic Brussels frite just as others claim Antoine (Place Jourdan/Jourdanplein) remains the king of the local french fry. No matter which fritkot you're at, try to be adventurous and have something other than ketchup or mayonnaise on your fries. Of the selection of bizarre sauces you've never seen before, "andalouse" is probably the most popular with the locals.

FRITKOTS
Maison Antoine, Place Jourdanplein - tasty fries with a large collection of sauces situated on a square close to the European Parliament. You can eat your fries (frites) in one of the several bars/cafés that carries the sign frites acceptés. Vegetarians be careful. Fries are cooked in Beef fat.
Chez Martin. The small nondescript fritkot plonked on Place Saint-Josse/Sint-Joost (Saint-Josse-ten-Noode/Sint-Joost-ten-Node) and run by the calm and affable Martin is a serious contender for the best friterie in Brussels. You can eat your frites at the nearby Cafe Gambrinus and wash them down with a pintje or two. Martin is retiring on December 26, 2009, so the place will close after that date.
La Friterie de la Place de la Chapelle, rue Haute-Hoogstraat (near Les Marolles). Another personal choice for the best frites in Brussels: the big chunks of potato, fried golden, and served with the usual dazzling array of sauces.
La Friterie de la Barrière, Rue du Parc-Parkstraat (just off the Barrière de St-Gilles/Bareel van Sint-Gillis). Golden and crispy frites - just the way they should be. This exterior of this fritkot also serves as mini-museum with several tracts, articles and other literature on the fronts and sides of the shack on the good ol' Belgian frite.

Delivery
Brussels online delivery could be enhanced significantly with the acceptance of some services on the web, however local businesses seem reluctant to join such websites and are hesitant to commit themselves to specific delivery times and the enhanced business such services would provide. In the meantime actually going to restaurants in person remains the best option for hungry travelers.

OTHERS
Arcadi, rue d'Aremberg-Aremberglaan 1B, just at the exit of "Galleries de la Reine", in the direction opposite to the Grand-Place - a quirky combination of old and new, the menu ranges all over the place but the reason people flock here is the selection of over 30 sweet and savoury pies (tartes). A slice big enough for a meal, served with salad, costs ?4-6.
Snack Pizzeria Porte de Halle, Avenue Henri Jaspar-Henri Jasparlaan, 134, directly across the city ring from Porte de Halle-Halsepoort. The gentlemen running the place speak a little bit of English and serve the best donar kebap and pizza in the neighborhood. The #39-Pizza Porte De Halle is probably their best pizza. Tel. 02/534 0051; Open 11:00 - 23:00 w/free delivery on orders over ?10
Sel et Sucre Creperie - Glacier, Avenue des Celtes-Keltenlaan, 4, near Merode subway station, Parc du Cinquantenaire-Jubelpark and the Arc de Triomphe-Triomfbloog. The fantastic crepes and friendly service makes up for the ordinary decor and just around the corner from the Arc de Triomphe-Triomfbloog. Open 12:00 - 22:00.
Mamma Roma, 3 shops: Flagey (Chaussee de Vleurgat-Vleurgatsesteenweg 5), Chatelain/Kastelein (Rue du Page-Edelknaapstraat 5) and Place Jourdan/Jourdanplein. Small pizzeria for eat-in (bar-style seating) or takeaway, sold by weight. Delicious crunchy base and some unusual toppings (one was spicy with walnuts, very tasty). Long queues but speedy service, deals available for pizza + drinks.

Mid-range

Brussels' tourist restaurant gauntlet can be found in Rue des Bouchers-Beenhouwerstraat, just to the north of Grand Place. The place has a bad reputation for waiters imposing themselves on passers-by, trying to lure customers into their restaurant. The authorities are aware of this, and are trying to take measures. Some restaurants may also tempt you with cheap prices for the menus, but when seated, the item on the menu happens to be unavailable, and you're forced to accept another, noticeably more expensive dish. Often, the exaggerated price of the wines will also compensate for the attractive menu. Knowing this however, you may be able to negotiate a better deal before entering.
A few restaurants stand out from the crowd though:
Aux Armes de Bruxelles, Rue des Bouchers-Beenhouwerstraat 13, +32 (0)2 511 5550. Closed Mondays. Basic honest food, including some very decent moules. Crowded, although worth the wait.
Chez Léon, Rue des Bouchers-Beenhouwerstraat 18, +32 (0)2 511 1415, [66]. Now franchised into France as well, this is the original and while it's huge and looks like a tourist trap, the moules are excellent and it's packed every day. Moules, beer and a starter will set you back ?25, and kids eat for free.
Scheltema, Rue des Dominicains-Predikherenstraat 7, +32 (0)2 512 2084. Specializes in fresh and tasty seafood.
Outside the Rue des Bouchers, you may try:
Au Pré Salé, 20, Rue de Flandre-Vlaamsesteenweg (near St Catherine square), +32 (0)2 513 6545. A former butcher shop, locals flock here for some of the best moules in town, sold by the kilo (figure on ?24) and served up in half a dozen ways. Also serves the full range of other Brussels favorites.
Falstaff, 19, Rue Henri Mausstraat 19 (by the Bourse-Beurs). Has cheap and decent food and is open every day until 2AM, around ?20-30.
Le Beau Soleil, Rue Joseph Lebeaustraat 7 (Sablon area). This tiny restaurant (approx. 14 seats) looks like a violin workshop, so you sit next to all the tools and half finished violins. Unlike other Belgian restaurants, it is open from 9AM to 5PM (Mo-Fr), 9AM to 6PM (Sat,Sun), closed on Wednesday. The menu is small but really delicious. The atmosphere is informal and friendly.
Les Brassins, Rue Keyenveld-Keienveldstraat 36, Ixelles-Elsene, +32 (0)2 512 6999. Its crowd is mostly made out of young couples or students. Rich choice of beer, with more than 50 varieties on the menu, and good quality of food.
'T Kelderke, Grand'Place, 15 Grote Markt, +32 (0)2 513 7344. ?9-19 Main courses. ?8.50 Plat du jour. Well-made typical Belgian fare. Try the carbonnades à la flamande (Flemish beef stew) & mussels. Note that this place can feel cramped when full of diners.
Close to the Bourse Jules Van Praetstraat (rue Jules Van Praet) is another rapidly developing street of restaurants and bars. Those of note include:
Lune de Miel, +32 (0)2 513 9181. Some very tasty Thai and Vietnamese dishes served in a fine decor.
Shamrock, +32 (0)2 511 4989. Its exterior and misleading name belie a great range of individually cooked Indian food. Get to know the owner and he'll treat you like an old friend.
Thanh-Binh , +32 (0)2 513 8118. The restaurant is very popular amongst the Euroworkers and business types common in Brussels and serves good Thai food. It can get crowded and is often noisy but is well worth a try.
Place Saint Catherine is also a popular area, and once the fishmongering centre of Brussels. While many of the fish shops have moved elsewhere, it is still home to many good seafood restaurants featuring lobster as a specialty.
Restaurant Vismet, Place Sainte-Catherinplaats 23, +32 (0)2 218 85 45. A small bistro that really gets busy after 19:00. Very good seafood. The handwritten menu can throw foreigners off, but everything on the menu(s) are top notch. Appetizers: around ?15; Main dishes: ?18-30
Jacques, Quai aux Briques-Baksteenkaai 44, +32 (0)2 513 2762. An authentic old bistro, with a charming kitsch decor. Very good fish.
Viva M'Boma, Vlaanderenstraat-Rue de Flandre 17, +32 (0)2 512 1593. For real Belgian home cooking. Terrace in the summer.
It is outside the touristic centre that the best deals can be found. Here are a few addresses in the Upper Town and Louise Area:
Madou's Provence, Rue de la Presse-Drukpersstraat 23, +32 (0)2 217 3831. Closed Saturday noon and Sundays. Innovative southern French cuisine at affordable prices.
Chez Oki, 62, Rue Lesbroussart-Lesbroussartstraat, Ixelles-Elsene. French-Japanese fusion cuisine in a modern decor. The chef has worked for prestigious restaurants in Paris. Reasonable prices.

Splurge
Belga Queen, Rue du Fossé aux Loups-Wolvengracht 32. A restaurant within an old, restored bank building. Has an oyster bar, gorgeous bathrooms (with strange stall doors), and a cigar bar housed in the old bank vaults. A good looking younger crowd seem to enjoy this place, and don't miss the offbeat restrooms.
La Belle Maraichere, Place Sainte-Catherineplaats 11, +32 (0)2 512 9759, closed We-Th. A classic fish restaurant. Very fresh fish and good old traditional cooking.
Les Larmes du Tigres (Tears of the Tiger), Justitiepaleis, de Wynantsstraat 21, +32 (0)2 512 1877, closed Tu. Upmarket and stylish Thai restaurant found just behind the Palais de Justice and better than most food found in Thailand.
De Gulden Boot (la Chaloupe d'Or), 24 Grote Markt (Grand Place) - One of the most famous restaurants in Brussels, situated on Grand Place. Beautiful old building, but too much of a tourist trap. And even after a ?200 dinner, you will get charged ?0.50 to visit the toilet.

Vegetarian
Forget about eating out if you're strictly vegan. There are some vegetarian restaurants that might cater without animal products though:
Dolma - A very nice vegetarian buffet Monday till Saturday from 19 till 21h. Chaussée d'Ixelles-Elsenesteenweg 329. Reservation 02/6498981.
La Tsampa - An organic/vegetarian shop annex restaurant, closed on Saturday and Sunday. Rue de Livourne-Livornostraat 109.
L'Element Terre - Located in Ixelles-Elsene, L'Element Terre features an ecclectic menu and wonderful, attentive service. Chaussée de Waterloo-Waterloosesteenweg 465.