I can't believe Beattie Feathers, the NFL's 1st 1,000 yard rusher (8.4 YPC), hasn't been mentioned.
Jim Brown has to be the all-time numero uno. Despite what anyone thinks of the level of competition then, he was doing things that no one had ever done, and no one he was playing with was doing. There were only about 4 or 5 1,000 yard seasons in the history of the NFL when he came onto the scene, and no one had ever rushed for more than 1,150. Brown came along and averaged, AVERAGED 1,368 per season. He led the NFL in rushing in 8 of his 9 seasons, and averaged over 400 yards per season more than the 2nd leading rusher in each of those seasons. That's kind of like Babe Ruth hitting more HRs than entire teams good.
The rest of my list is just going to have to be guys I've actually seen play.
#2 has to be Earl Campbell. Probably a bit biased here since he's probably my all-time favorite athlete in any sport. Much is made of Earl's bruising style of running, but he had speed too. Never forget him outrunning the Dolphins DBs in the 4th quarter of the Monday night game. And unlike Emmitt who ran behind an all-pro o-line, Earl had the likes of Conway Hayman, Carl Mauck, Ed Fisher and Morris Towns. With that line and everyone on the planet knowing Earl was getting the ball, he still couldn't be stopped.
3 - Emmitt Smith
4 - Eric Dickerson
5 - Walter Payton
6 - Tony Dorsett
7 - LaDainian Tomlinson
8 - Barry Sanders
9 - Adrian Peterson
10- Shawn Alexander
Alexander?? Yes. He had a nice little 5 year run where he averaged over 1,500 yards and 17 TD per season. Not many with a run like that, including the guys on my list.
Barry would be further up my list but it seemed like every time I watched a Lions game he'd have so many plays where he lost yardage, then he'd bust one for 50+. Even with the numbers he did put up though, with a little better team around him, it's scary to think of how much more he could have done.
And another 3, 4 year run at his 2010-2012 level of play, I could have put Arian Foster on that list. He could do it all and was fun to watch. Sucks that he couldn't stay off the trainer's table.