Throne of Glass series by Sarah J. Mass. If memory serves me correctly, a friend introduced me to these books after I finished The Mortal Instruments series and didn't know what to do with my life. The Throne of Glass series is Adult Fantasy complete with assassins, fae, witches, kings, and demons. It's full of suspense with a little bit of romance and good mix of wit and humor.
As with any long running series where one is waiting a year or more for the next book, I was a few chapters in before I remembered exactly what was going on and with whom. (There are several prominent characters and their stories all intertwine, so I had more than a few moments where I was staring off into space trying to remember what had happened previously.)
I have a hard time putting this book down ("Sleep? Oh, do I need that?") and I'm sure I'll be finished within a week. Then... I can start waiting nearly another year for the 6th book. *sigh*