One of the books I'm waiting for (and I love series, so there's a lot... lol), is the next book out in Cassandra Clare's Mortal Instruments series: City of Lost Souls, which is due on May 8. It's the fifth book in the series and I'm enjoying this series so much that I broke one of my own rules and paid full price for the next Nook book in the series when I finished the first one at 11:30 at night!!
The Mortal Instruments is a YA Urban Fantasy series that will eventually have six books in it. There is a companion series Infernal Devices which takes place in the same world, but about 100 years earlier.