Kobo (UK at any rate) has a number of SF and fantasy titles reduced in price for a week, and not just the aforementioned
The Collected Stories of Arthur C Clarke.
Due to the nature of the URL it could be that the address will change often, so instead I will direct you to the
front page, where you should click on
Out of this world savings on Sci-Fi & Fantasy in the top banner and then on the
Browse now button.