I'm pretty sure this is a glitch freebie, but 7 highly-specialized textbooks from academic publishers Springer & Aspen have shown up at £0.00 in the Amazon UK store, and some of them also seem to be available in other regions as well (at least to Canada).
Subjects include Food Chemistry, Semiconductors, Nanotech, Elecronic Design, the future of small telescopes in the new millenium (these ones look like they might be intended to be free, as their digital list price is set to £/$0.00 and you don't "save" anything like you do with the others).
Linkage for the lot for the UK:
Springer,
Aspen
Linkage for the lot for the main store:
Springer,
Aspen
Enjoy while it lasts, and be absolutely sure of the price before 1-clicking, because the prices for the probably-glitch ones run into triple figures.