I get enewsletters from the following:

Book Sends
Ereader News Today
Free Kindle Ebooks (longest list, WAY more uncurated on their website, and they have a UK option)
Freebook Sifter (just discovered this about 10 seconds ago, haven't checked it out)

Like Labby said, you have to make sure the book is free in your country. Watch for that!!

Cheers...

"It's the mythology of a sun god who wished he was a man because he saw something so great in us.
It's the story of a hero who could move whole worlds and see through stars and hear a whisper on the other side of the planet...
...and who fell in love with a storyteller." - ashmaht (x)