There's a decent selection of eBooks on offer at Amazon.co.uk at the moment, covering a good spread of science fiction & fantasy genres:
Books for 99p:
The Ocean at the End of the Lane by Neil Gaiman - Another short standalone bestselling novel full of mysticism and stories.
Senlin Ascends by Josiah Bancroft - The self-published hit that some people think would have won a raft of awards if traditionally published.
The Last Wish by Andrzej Sapowski - A collection of short stories that launch the Witcher series
Whispers Underground by Ben Aaronovitch - The 3rd book in the Rivers of London series
The Day of the Triffids by John Wyndham - The classic SF novel
Empire Games by Charles Stross - The first book in a new series set in the Merchant Princes world.
Defiant Unto Death by David Gilman - The 2nd historical fiction book in the Masters of War series, set during the Hundred Years War.
Books for £1.99
The Truth by Terry Pratchett - The 25th Discworld novel, the one where they discover printing and newspapers
Star Wars: Thrawn by Timothy Zahn - The character many people should have been the basis for the new Star Wars film reboot.
I'm sure there are a few more, but those are the ones I've put together for today. Heads up that I don't know how long any of these are on offer for!