www.ereaderiq.com
Very handy, lets you sort by timeframe and limit genre to your liking. If there's a flaw, it's that some books get placed in mysteriously wrong genres at times.
They also have a service where you can identify a book, and they will email you when/if the price drops by the amount you specify. I've tried it, haven't gotten a 'hit' yet (for one of the books I really wanted, but missed, when it went on promo.)
KentE