It's a reliable online restaurant guide that also has background info e.g. a recurring piece on Spanish food and wines. Useful for general info and also for making online reservation. Check it out.
I can recommend the following as good, interesting quality restaurants offering good food or great atmosphere and sometimes both at reasonable prices: Lamucca in the Malasaña district, Orixe and La Camarilla both in La Latina and Chic and Casa Gallega near the Opera. For a decadent champagne/cava experience Bar Privee on the edge of the (in)famous Chueca area is hard to beat.
It is a good restaurant guide for Madrid. I can personally recommend the following restaurants: in the La Latina area Orixe (Galician cuisine), La Camarilla (trendy place to be seen with good tapas and innovative main courses) and for a taste of the Canary Islands try El Escaldon. Near the Opera there's the trendy (and good) Restaurant Chic and the more traditional Casa Gallega (another Galician specializing in seafood). A great place for pre-clubbing food and great fruit cocktails (with or without alcohol) is Korgui. More off the beaten track is the respectable El Olivo and more intimate and up beat Memento, also does a great Sunday brunch: other good brunch addresses include La Camarilla and Cafe Oliver. For that decadent night of cava or champagne (and great food) the place to be is Bar Privee. Have fun!
A good restaurant featured in the guide is Mercado de la Reina: good value for money and popular with the locals.
DiningCity has revised and updated all of its international sites. It's now even more reliable and attractive. A good source of local information about a range of quality restaurants.