The Harlequin Set and other stories by Agatha Christie is available for 0.99 at Amazon ( This is a US only pre-order, it is released in august. And it is 9.99 at BN) 


Map of Bones by James Rollins is free at Kindle and BN (This is US only.  And Sony is not included, so I cannot download it. ) 
But, I did discover that the omnibus of The Doomsday Key and The Last Oracle  is discounted to 2.99  at both BN and Sony, which means Amazon should have the same price. 

 Simon and Schuster offers a bundle of three Joy Fielding novels for a free at Amazon.

The Perfume of The Lady by Gaston Leroux is available for 1.35 at Booksonboard. It is unlikely to end up at Amazon, since it is published by Sterling Publishing which is owned by BN.
 This the second book in the series, and I recommend that you read the first book before.  It is in Public Domain and can be found here. 

 Open Road Media has a summer sale, with some interesting titles.  
Kobo also offers an coupon code on Open Road mysteries.