Beers: Poechenellekelder. They do a good lasagne, but it's no haute cuisine. Beer selection is fantastic and the waiters are extremely knowledgable. It looks touristy but I promise you it's brilliant, and not massively expensive considering its location. Perhaps not for dinner if that's your main focus of the evening though.
Seafood: Scheltema. Not cheap, but not Michelin star prices either.
Belgian grub: Fin de Siècle on Rue des Chartreux. Quality dishes (including steak, jambonneau, ribs..), huge portions, decent beer selection and quite frankly, cheap. Queue usually goes out the door on a busy night but worth it (can't book a table).
Restobières has good grub with a wide selection of beers (usually in the dishes), and In 't Spinnekopke is a common restaurant for people who organise small beer tours, although I've never been personally.