What's your favourite book series?

has to be the sisterhood of the travelling pants. it's written at a sorta young level, but each character encompasses all of what teenagers girls think and feel. it's wondrous.

Darren Shan all the way. Then Stephen King's Dark Tower series. HP + LOTR somewhere behind that. Oh and the Unfortunate Events series.
Do we include trilogies in this?
Oh boy. This is a hard choice. Ever since I was young I've read the Redwall series. I might ahve to say those are my favourite series, though "His Dark Materials" by Philip Pullman is a wonderful trilogy. I love the Narnia books too and have read those countless times as well. Those are the oldest trilogy I love. My parents read them to us in the car on long trips.
Hm... I love the Harry Potter series, and ofcourse the Alias books. The Narnia books are good too. But I love the Deptford Mice Trilogy by Robin Jarvis. Oh, and I love the Twilight Series by Stephanie Meyer.