I have to echo the recommendation for the dining room at Hotel Grano d'Oro.
The hotel recently underwent a substantial expansion, adding five rooms, a conference center and a major expansion of the restaurant.
Prices for entree's (everything is a la carte) run from about U.S.$6.50 - $18.00, with most in the thirteen dollar range.
Their wine list is excellent for Costa Rica, with a few rare Chilean gems for around ten bucks a bottle.
For novo italiano, I love Cafe Mundo (right around the corner from the Sportsmen's Lodge.
For pan-Asian, Tinjo is an excellent, but far from the only choice. Don Wang can be spectacular, as can the Japanese restaurant at the Hotel Trip Coribisi.
The Japanese restaurant in the Trip Coribisi features a private dining room where one sits low to the floor on tatame mats. The decor and the food is authentically Japanese, the prices are typically padded expense account huge.
Fabulous Peruvian food is available at Machu Pichu, across from Oasis massage parlor on Paseo Colon. They make a sea bass that will make you cry. Drinks BTW are generous and the service is at worst a C-plus (high marks for Costa RIca).
I agree with Orange about the Colonial. Their food is excellent, and if you order from the "bar menu," the prices are very reasonable. As Orange pointed out, they'll try to give you the tourist menu first. Request the other menyu; you'll save 20-30% off the tourist menu prices!
There are a number of restaurants I'm eager to try: Mirador Ram Luna , Esquina de Buenos Aires, Bacchia and the White House, just to name a few.
That being said, I'd still like to try Mariscar, JR Ribs, Pollo Campesino and some of the other lower-priced restaurants. I've heard good things about the burgers at both the New York Bar and The Hamburger Factory, neither of which I've yet to try.