This post is a little late, but Prologue Books, which is a subsidiary of F+W Media is offering two free eBooks for Nook and Kindle. The titles: The Screwball King Murder by Kin Platt, and The Evil Friendship by Vin Packer. They are both available until July 1, 2012.
If you are unfamiliar with Prologue it is a real treat. It has issued dozens (probably hundreds) of genre classics--crime, western, science fiction and fantasy--in eBook format. A few of its authors are Robert Colby, Vin Packer, Talmage Powell, Wade Miller, Peter Rabe, Jack Webb, Louis Trimble, and Mike Barry (Barry Malzberg). The books range between $3 and $4, and bring a fistful of entertainment. You can check out Prologue's catalog at it website--here.
The Screwball King by Kin Platt. Platt is an author I'm unfamiliar with, but it appears to be a pretty good sports mystery. It was originally published in 1978 by Random House and features private investigator Max Roper. If it's good, Prologue has an impressive list of Platt's work available.
The Evil Friendship by Vin Packer. Packer is a known quantity. Her work is among the best produced in the mystery / crime genre in the 1950s and 60s. Friendship was originally published in 1958 by Gold Medal, and you really can't go wrong with a freebie.