The best YA book I've read in a long time is _Holes_ by Louis Sachar,
which I find entertaining and technically impressive, with intertwining
stories across three points in time, nobody acting out-of-character
stupidly for the sake of the plot, and as far as I could tell, no dangling
plot-holes or unexplained coincidences. It was a very satisfying tale. The
movie (amazingly enough) does it justice, but the book is better (more
detailed) than the film.

I also have to plug Lemony Snicket's _Series of unfortunate events_
They're gothic humor for kids, and incredibly witty -- a word which here
means "droll in an erudite manner."
Don't be put off if the first couple books may seem somewhat repetitive,
because (a) they're quick/short -- I've read several in a single evening,
and  (b) he's establishing the pattern to lull readers into comfort and
then pulls the rug out in Book 5.

More interestingly, from an adult perspective, there's a growing
meta-mystery developing as the series progresses. Little clues, in hints
and asides, and then (after book 9) he came out with the _Unauthorized
autobiography_ in which he reveals a conspiracy extending into preexisting
books (but still doesn't quite answer the IMPORTANT questions). It's like
Illuminati for kids and it's a lot of fun.

You can get a good feel for the series at http://www.lemonysnicket.com/
and, to his credit, you can read the introductions and opening chapters
for free to evaluate them.
For the 1st book, intro: http://www.lemonysnicket.com/books_bad.html and
1st chapter: http://www.lemonysnicket.com/ex_bad.html

[BTW, for folks in the Boston area, I bought a copy of the first book
specifically for lending, so ask up]

--
     ------> Elisabeth Riba * http://www.osmond-riba.org/lis/ <------
     "[She] is one of the secret masters of the world: a librarian.
      They control information. Don't ever piss one off."
                                   - Spider Robinson, "Callahan Touch"