I started reading "The Hobbit" to my oldest son when he was about 4. He loved it. What astounded me, though, was that his little brother, who was only two at the time sat and listened with great intent. I didn't do the voices, but in retrospect, I should have. I realized later how much fun it was.
Of course, maybe I shouldn't have been surprised. When we bought my second son the hard-bound original stories of Thomas the Tank Engine, which was filled with wonderful art, he literally sat and paged through it for like 45 minutes straight. And he wasn't even 2 yet at the time.
I also read my kids "The Wizard of Oz", all the original "Winnie the Pooh" books, "Charlie and the Chocolate Factory" and many others, including the usual short-form kids books like Dr. Seuss and P.D. Eastman when they were really little. I miss reading to my kids, but eventually we couldn't all fit in the bed together... (Plus, they're all adults now.)