Hmm....that's a toughie. I read a lot, but I'd have to say the one that stuck with me the longest in my memory was the books written by the late Brian Jacques.
He wrote the Redwall series, a loosely connected series spanning several hundred(?) years about anthromorphic animals in a somewhat medieval setting. It's cooler than it sounds, haha.
He also wrote the Castaways of the Flying Dutchman trilogy, but I'd only recommend that for older readers. Gave me nightmares when I was little...