Young Adult / Adult Fantasy

Despite the less than stellar quality of literature, I found that I greatly enjoyed series such as Harry Potter and His Dark Materials because I could immerse myself in the story and be very entertained by them. For example, When I picked up HDM, I read all three books in less than 3 days, and then went on the wikis and the community forums and took in as much periphery information as I could.

Can anyone recommend fantasy books or series which will have this effect with the added bonus of being high-quality literature? What is the cream of the crop for the fantasy genre?

Try the Bartimaeus trilogy by Jonathan Stroud.  I'd compare it to HDM.