There is no real theme this week.
BN launched their Nook for Web earlier this week, and as a part of the launch they offer 6 free books.
Moira Rogers offer several free e-books, some through their webpage, others through stores.
As a part of the promotion for Joss Ware's upcoming release, Beyond the Night, is discounted to 1.99 at all major stores.
The Bride and the Brute by Laurel O'Donnell is free at Smashwords.
Edit: I just discovered that if you like mysteries, there is some nice deals over at Books on Board.