There is talk around baseball that Miguel Cabrera could be the greatest hitter of all time. He is a tremendous hitter, but I do not think he is the greatest yet. He could become the greatest right handed hitter. To me, the greatest hitter ever is Ted Williams.
Willams finished his career with 521 career homeruns, 1839 RBIs and with an average of .344. He also won two triple crowns, six batting titles and two MVPs. He did all this while missing all of or part of five seasons because he fought in WWII and the Korean War. These were prime years also, three of which came immediately following winning his first triple crown. Here is his career stats
Couple other notes on Willams. Beyond his baseball accolades, he was known as a very good wingman as a fighter pilot for John Glenn during WWII and also is a member of the International Fishing Game Association Hall of Fame. Williams also was a tireless worker for the Jimmy Fund-a Boston based charity that helps cancer stricken kids.
Anybody wants to learn about hitting, he wrote a book called "Science of Hitting".
Here is a great interview Williams did reflecting on career and life with Bob Costas that originally aired in the summer of 1993: