I just finished The Mysterious Benedict Society by Trenton Lee Stewart (Little Brown, 2007; check out the book's website here).  It took a lot longer than it should have--I kept leaving it upstairs where the children were sleeping, or downstairs after I went to bed myself, and at one point I had to return it to the library (it was overdue) and check out another copy.  Maybe I just didn't want it to end.  I love puzzle-mysteries, and this one has a great cast of characters, too.  Here are the four gifted children who form the society, working on an assignment:

The children--all except Constance, who was too busy humphing--set to their notes.  Sticky read so quickly that he seemed hardly to have started before he'd finished.  He sat quietly, deep in thought, waiting for the others.  Ten minutes later, Reynie had finished, too, and Kate, noting this, set aside her last few pages and asked the boys to fill her in (132).

Look at how Stewart identifies each of those characters in that one paragraph.  My favorite of the four has to be the diminutive Constance Contraire.  She felt familiar right away, although I didn't realize why until the end of the book [no spoilers here].  Here's a description of Constance:

Constance's face turned so red, her pale blue eyes glistened so brightly behind angry tears, and her wispy blond hair was in such a state of dishevelment that she looked more like a small child's painting of a person than an actual person herself (227).

I also love the ink and wash illustrations by Carson Ellis (on the cover, and at the beginning of each chapter).  The second MBS book (The Mysterious Benedict Society and the Perilous Journey) will be out in May, with illustrations by Diana Sudyka.  Can't wait.  I wonder if Trenton Stewart Ellis is a fan of the Decemberists?