The Book Depository (Online Book Store, UK)

  http://www.bookdepository.co.uk/

The Book Depository is a British online book store that sells all types of books, e-books, comic books, stationary and some fun esoteric stuff (tarots, pendulums, etc.). They have a humongous volume of books, mostly in English, but also in other languages, Spanish included, sold at very competitive prices. They have frequent discounts and offers, so you get the best possible deal on the book of your interest, whether is a best-seller or a rare book. Actually, their focus is not on the bet-sellers, but on both these and rare books, or those edited by small editing houses.

The shipping is done by Post mail, for free anywhere in the world, no matter how much you spend in your transaction! The shipment is quite fast, and the delivery takes the usual days that you would get a letter/parcel from the UK to your country, not more not less.
I am very pleased with the service, prices and the incredible variety of books and stationary they have. Many times cheaper than in Australia, and with books that we would rarely find here in normal libraries.

The only down of the service is their tracking system, which only tells you when your order went through and when it was shipped, which is not much, really.

The site was recently bought by the Amazon Corporation, although they are still operating following their usual prices and policies, which is much better than Amazon book-store does operate.

I will certainly shop with them again.