By Jonathan Stroud. Book one of the Bartimaeus trilogy.
This book does not live up to the hype. If you're expecting something wittily and drily humorous, well, I laughed at a few lines, but overall I'd say Pratchett does the job much better. Bartimaeus comes across as rather petty and mean at some points and unfortunately does not develop the sort of relationship I was expecting with Nathaniel.
The book does come to a definite conclusion even if there are a ton of loose ends left behind for the rest of the trilogy to weave together. However, there also seem to be some contradictions relating to the practice of magic. (Both characters seem to agree that all of a magician's power comes from summoning demons, so how then do they do other things like fire and lightning bolts, which don't seem to be directly related to summoning? And what about the prison spheres used on errant djinni?) Nathaniel's character also seems promising at first, due to his precocious magical ability, but by the end he too seemed somewhat petty and indisputably deluded.
I don't really want to read the rest of the trilogy, but I might just to see if it turns into anything better.