Founded in 1858, Casa de Diego is a store where they sell Spanish fans and parasols/umbrellas. You'll recognize the store because of all the fans in the window. The fans are gorgeous, even if some can be expensive. When you buy something, they also wrap it up nicely in their company wrapping paper.
What to buy: Fans, parasols, umbrellas.
San Gines second hand bookstore is a well known establishment of Madrid's centre, and as the book worm that I'm, I like to browse the books they offer from time to time, looking for something new (or second hand, who cares) to read, and for a good chat with the owner of the library, a character as notorious as the shop itself.
What to buy: Basically, second hand books, though they also have postcards and posters of Madrid at good prices.
What to pay: Books are less expensive than in regular stores. In the unlikely even that you'd find the prices not low enough, a little bit of bargain had never hurt anybody ;-)
In Cuesta de Moyano, a little street between Atocha Station and the Retiro park (Metro Atocha) you can find some old Madrid maps and engravures that could make an original souvenir.
Better on sunday mornings, when all the stands are open.
This used bnooks market is located in "Cuesta de Moyano" street, between the Atocha Station and the Retiro Park.
Is open mostly on sunday mornings, but some stands are open on weekdays too.
What to buy: Here you can find books (most in spanish), magazines, posters, old engravures...
What to pay: Books from 1-2 euros
Museum Musei is a shop specialized in reproductions of museum items. Here you will find from books on Art to mugs with Goya or Velazquez paintings on it.
There are many, I think one is at Velazquez Street, and there is one at the Barajas airport Duty Free.
What to buy: Nice items for souvenirs, from pencils to scarfs, umbrella, creamics...
If you are looking for Books, CD... this is the place . A huge variety, good prices and a lot of original versions. A whole building for all kinds of cultural shopping. They have a section where you can listen at top10 hits. Tickets for concerts sold here too.
What to buy: A ggod place to buy english / french original books
What to pay: Open on sundays too.
Four floors of music, CD's and books. It is a huge store, and on the top floor it's possibly to find English books as well.