To launch their line of ebooks, the Black Library is offering free ebooks every Friday for five weeks. They're available in mobi and epub format (Kindle and Sony compatible, respectively, though obviously lots of other devices can read those formats).
The first book available is First and Only by Dan Abnett, from the well-regarded Gaunt's Ghosts series.
The files are zipped, which means Kindle users will have to download them to a computer first, rather than installing the book straight from the Kindle browser – but that's a small price to pay for a free visit to the year 40,000.
The Black Library isn't planning to sell its books via the Kindle Store on Amazon, so don't look for them there. They'll be sold direct from the Black Library website.