The Sisters Grimm by Michael Buckley and The Man of My Dreams by Curtis Sittenfeld

My nine year old just finished this(Thank you Danzel for recommending it!) - and wants the next one. I think its just about right for his age and reading level. We got about five nights from it, so pretty good value for money(often recently I've bought him books that he finished in an evening  - which is expensive!) and he spend this morning in bed with our Grimms' Fairy Tales looking up all the characters mentioned by the fairytale detectives.
While he was doing that I was downstairs finishing this..

..which is probably not great value for money as I only purchased it yesterday, but I LOVED it. I've loved everything I've read by Curtis Sittenfeld (see review of Sisterland here) and even though I realised just after starting this that I had read it before, it didn't matter, it was still a great read second time around.