i guess it's Goosebumps by R.L Stein
it's the first novel i read, in which you could actually choose how you want the story to be. it can be a lot of fun :D
More than Human by Theodore Sturgeon had a pretty amazing concept, even if it's kinda hard to read.
Invisible Cities and Cosmicomics by Italo Calvino also had pretty great concept, I enjoyed them.
There's also Slaughterhouse-Five and Breakfast of Champions by Kurt Vonnegut, they're funny novels with interesting concept. While Cat Cradle was good, it wasn't as funny.
A Christmas Carol by Dickens, I kinda read the abridged version with illustrations. It's a simple story, with a powerful message.
and yeah, this one's probably one that most of you haven't heard. it's not really a novel, more like a self-help book, but it's written like a story. the title's Discover Your Destiny by Robin Sharma. i read several of those series, but this one left the deepest impression on me.
For the best novel I've read, I don't think I can pick one. While being enjoyable was enough to make it good for me, I still hadn't found something that completely changed my life for the better, and let me achieve my dreams, no matter how impossible it may seem.
I think, the perfect story is something that will bring me from zero to something much more, and my life won't stay the same again. while i might be placing my hopes too high, i believe, one day, that story will come, or maybe i eventually write it myself.