Recently I have been very into young adult literature. I feel quite grateful that my children will have access to such a wealth of choices since when I was a teen/tween the choices for books was limited. Once you got outside of The Babysitter's Club and Nancy Drew, there was not a prevalence of great young adult series. The few others that did exist tended to have a sci-fi/fantasy spin making it clear that the only people who read silly old books were probably only doing it between advanced calculus classes and LARPing practice. Now, probably thanks in large part to the Harry Potter phenomenon, there are tons of great options, many still in that genre, but somehow popularized.
Currently I am reading the Fablehaven series by Brandon Mull. The books follow two youngster who discover that their grandparents run a preserve for magical creatures. Part mystery, part coming of age story and part adventure series these books are a wonderful read. I won't tell any plot because really, you need to check these out and experience them for yourself. Written at the same level as the Rowling tomes, these are a quick read for adults and a nice level for kids who are ready for some serious length/material, but perhaps not full on Twilight ready. I think of these as a great precursor to the Xanth series by Piers Anthony. (All you other dorks say Hayyooooo.) Check them out, though if you are like me, you will have to wait your turn since the kids here are avid little readers and often (if you can even imagine) have the books I want checked out. Darn, exceptionally literate, whippersnappers.