I just finished reading Madhouse by Rob Thurman. It's the third book in her series about Cal and Niko Leandros. Cal (short for Caliban) is part monster. His mom was human but his father was a terrifying creature called an auphe. Niko is full human and he basically raised Cal. The brothers have been running their entire life from the auphe but they've finally settled down in New York City. They're started a supernatural clean up service with the help of Niko's vampire girlfriend, Promise. Their latest job is to hunt down a serial killer called Sawney Beane.
This series is really intense dark urban fantasy. The city is alive with monsters like boggles (they live in Central Park and eat joggers), nymphs, werewolves and other assorted fairy tale creatures. Things can get gruesome at times but I think the reason why I like the series so much is that Cal isn't perfect. He's a young guy trying to deal with the horrors he's seen in his life and he's an interesting mix of contradictions. If you like fantasy you should give this series a try. The first book was Nightlife and the second book was Moonshine .
By the way, an interesting note, Rob Thurman is a woman. Short for Robyn I believe. It makes sense based on the quality of the writing. I'm a little biased I think women tend to be better writers than men.