The Little Hump-Backed Horse
It's an illustrated Russian fairy tale by Pyotr Yershov. This book got me hooked to reading. It was funny, unpredictable and romantic -- an adventure story, written in verse! I didn't learn till I was quite grown up that the iambic tetrameter it used inspired Pushkin's Eugine Onegin, which in turn inspired Vikram Seth's The Golden Gate.