This guy is a spark plug for the ages. He may be the quickest legs in the history of the game. His website could use an upgrade but the impact he has on the game is unreal. If you have never seen him play try to catch 1 game with him.
http://www.ladainiantomlinson.com/home.htm

In his prime was like a dancer on the field. Check the video for a quality look back at his brilliant moves.
http://www.metacafe.com/watch/1474901/barry_sanders_highlights/

This guy is right behind Payton for skills and power through the middle. It would be a toss up but Smith is truly amazing. Check the video link.
http://www.youtube.com/watch?v=ITpe-AIztco

Was before my time but the numbers he put up were astounding. One of the best athletes in the history of all sports.
http://www.youtube.com/watch?v=1hL_zT5imfc

I was very young when I watched him play but what an exciting player who beat entire teams single handed. Truly amazing and in my eyes, the best RB ever. Some stats - In 13 seasons Walter Payton did wonderful things for the Chicago Bears. He could run, block, catch and throw. He was probably best known for keeping his legs moving and breaking loose when he appeared to be tackled. They called him Sweetness and we lost him way too soon when he died. He had 3,838 rushes for 16,726 yards, 110 tds and a 4.4 average per carry. He added 492 receptions for 4,538 yards and 15 TDs. All this while playing on some really bad Bears teams most of his career.
http://en.wikipedia.org/wiki/Walter_Payton