I just wanted to stop in and thank the assembled forces of Chowdom whose reports were so helpful in eating well on a recent trip to northern Spain.
We ate twice at Cal Pep, where the much-feared wait was only about a half-hour. We asked for a selection and did great--standouts were deep-fried artichokes and the final botifarra sausage on white beans. We had a no-shellfish, no-pork eater with us, and she did fine; they brought her a portion of the artichokes and a terrific oven-baked hake (merluza al horno), supremely garlicky and juicy. On another trip I'd make a point of asking for it. I won't attempt to match the luscious descriptions of the food given by others here--I'll only add my exhortations to make it a stop.
We had a good lunch, too, at Suquet de L'Almirall in the Barceloneta (Passeig Joan de Borbo 65.) The navajas (razor clams) were especially good here, meaty and plump enough to stand up to the serious grilling they'd been given.
As everyone said, it's hard to eat badly in Spain. We ducked into many bars for tapas and pintxos, and were never disappointed. Even the tortillas at the rest stop on the highway were pretty good!
One note: the horchata place in L'Eixample is not at the corner of Valencia and Bruc, as Jim says, but one block north.
We also spent a little while in Basque country, though we didn't get to eat as much as we wanted (long story). But we did have a terrific, simple lunch at Beitxi in the fishing town of Bermeo, about 30 minutes from Bilbao on the Atlantic coast. We ate txangurro (spider crab), merluza con kokotxas (hake accompanied by its tender, slightly slimy cheeks, in a gummy-in-a-good-way garlic and parsley sauce) and bacalao in vizcaina sauce. I'd recommend it to anyone who happened to be in this town (which is about 10 minutes from Bakio, the prettiest beach I've seen anywhere in Europe.)