You can't eat at Cinc Sentits or Moo for every meal (well, I can't), so here's my report on getting tasty everyday food in Barcelona... Anyone have other tips (or corrections)?
Pimientos del Padron (Boss Peppers): deep fried, but not breaded, small green peppers. Very mildly spicy, but sometimes you get a very spicy one. Like Russian Roulette with capsaicin instead of bullets. My favorite widely available tapa.
Berberechos a la plancha or al vapor: tiny tiny clams. In tapas bars, berberechos are usually canned, but if you see "a la plancha" or "al vapor," they're probably fresh, served in their own little shells, and they are (generally) amazing.
Raspas: breaded and deep-fried sardine bones. Not too common, but tasty and exciting. Makes a good "wierdest food you ever ate," if you're looking for a low-risk one. They're just crunchy and fried and fish-flavored.
Orejas de cerdo: Yep, pig ears. Apparently a specialty of Valencia, and not too common in Barcelona. In my experience, not really worth it. Made a better travel story than a snack, as I found them kind of rubbery and slimy.
Menu del Dia:
Most of these tips are for the 8-to-10 euro level (the most widely available). Pay more, get more. I had some very nice "menu" in the 12-14 euro range.
There will almost certainly be canned corn in the salad. Brace yourself.
The fish might be fresh and delicious, but it will be bony, and maybe scaly too. Menu is too cheap for the kitchen to filet or debone anything. I usually stick with meat, which is often a thin filet, quickly seared, juicy, and tasty.
Flan is a common dessert option. If it's homemade, it's probably pretty good, but it's often mass-produced. They won't be offended if you ask if the flan is house-made.
Menu is usually too cheap for the wine to be decent. And by "decent" I mean minimally adequate (I'm appalled by this, in the land of excellent, relatively cheap wine). I would recommend ordering a beer or a soft drink instead. If you do order wine, they might ask if you want "gaseosa" with it. It's like sweetened club soda, and people add it to cheap red wine to make it drinkable. Take that as a sign of the quality of the wine.
If you don't want a dessert, some places will let you substitute a coffee at no extra charge, but some won't.
Adequate bread is available on every corner. Good bread is harder to find. My favorite (widely available) bread is from Veritas, a natural-food market that has 8 branches in Barcelona <www.ecoveritas.es> Their olive baguettes are nice with wine and cheese.
There are grocery stores everywhere, but be aware that their meats and cheeses are barely adequate, and often processed and/or old. Shop in the markets or the independent cheese and meat shops to get the real deal.
The big markets (Boqueria, Sant Antoni, Santa Caterina, etc) are absolutely not to be missed for sightseeing, and can be great places to get fixings for lunch or a snack (municipal markets website: <mercatsbcn.com>). My market tips:
You can order sliced meats by the gram ("100 gramos de jamon dulce" makes a couple of hefty sandwiches). You can ask for manchego to be sliced (en cortes), you don't have to buy it by the hunk (un trozo). Pink ham (jamon dulce) can be excellent or terrible, and quality usually goes with price.
The salt cod stalls usually sell house-made brandade.
There are stalls that sell olives, boquerones, and other ready-to-eat bits that make good lunch-parts.
The vegetable and fish stalls will generally throw some free parsley in with your purchase if you ask for it.
If you ask for a chicken at a poultry stall, they will assume you want it cut up, and will grab a whole one and chop it up right there. They display them with the heads on, but don't worry, they don't give you the head (they might if you ask for it though, I've never tried).