Day 4 – Your guilty pleasure book.
Yep, this is me, cheating again... my guilty pleasure book would actually be movie & video game novelisations/tie-ins. In most cases I'll have read the books before seeing the film or playing the game and one of the endearing qualities of the tie-in book is that they're generally short fun reads, so excellent when you need something light and easy. They're also great for filling in the gaps of the story and fleshing out the characters.
Personal faves include Resident Evil (excellent for the movie versions but the VG tie-ins have jumbled continuity with the games which makes it...interesting), Tomb Raider (extra movie scenes! Wahey! Although, again, the VG tie-in books don't quite hold up as well), the Riddick books (arrgh, one of the names is wrong in the Pitch Black one!), Doom, the Mummy books, X-Men (novelisations of films adapted from comics! Hee!) and the Alien books. Indiana Jones novelisations and the odd Star Wars short story anthology do creep in occasionally too.
For more Day 4 fun, check out:
Floor to Ceiling Books
The Erudite Ogre