I have been speeding through Michael Buckley's "The Sisters Grimm" series. It's actually written for pre-teens, but it's very well done. It's about two sisters who are descendants of Jacob and Wilhelm Grimm, who discover that fairy tales are actually true, and that their grandmother is a detective who investigates crimes among fairy-tale folk.

For grown-up mystery, try P.J. Tracy's books; for supernatural mystery, try Heather Graham. I hope that you find something to capture your interest again--I've had similar problems after finishing certain books.