Over at SF Signal, they ask the same question. Thought I'd like to see what y'all say, mainly since my choices are crime related.
For me, it was actually three books, all used and found in a nice little bookstore, Books Abound, in Cypress, TX:
Stolen Woman - Wade Miller
Guilty Bystander - Wade Miller
Homicidal Lady - Day Keene
All three books are by authors I first was introduced to via Hard Case Crime. Branded Woman, Wade Miller's HCC entry, is one of my favorite books HCC has ever published. My review of Keene's Home is the Sailor is here.