I would like to recommend Thomas E. Sniegoski's Remy Chandler series. It's about an angel that turns his back on Heaven after the war with Lucifer and tries to live on Earth as a human. He basically wants to be left alone but keeps getting dragged into these epic struggles. The books are kind of a cross between the Dresden Files books and the
Supernatural TV series.
There are four books out so far with a fifth coming out in August.
http://www.sniegoski.com/remy/
He's also written a YA series called The Fallen. I haven't read them yet but my son really likes them.