I wouldn't take a runningback in the first round unless I believed him to be a once in a decade type player. Runningbacks are a dime a dozen at this point. Just draft offensive linemen and pick up a runningback later and/or sign one. There are so many good runningbacks that enter the league every year and many can be drafted after the first round.
After 1st RB's
Le'Veon Bell, 2nd round
Demarco Murray, 3rd round
Justin Forsett, 7th round
Eddie Lacy, 2nd round
Jeremy Hill, 2nd round
CJ Anderson, undrafted
Giovanni Bernard, 2nd round
Andre Ellington, 6th round
Lesean McCoy, 2nd round
Matt Forte, 2nd round
Alfred Morris, 6th round
Arian Foster, undrafted
Frank Gore, 3rd round
Joique Bell, undrafted
Andre Williams, 4th round
Lamar Miller, 4th round
Jamaal Charles, 3rd round
Chris Ivory, undrafted
Tre Mason, 3rd round
1st round RB's
Marshawn Lynch, 1st round (12th)
Jonathan Stewart, 1st round (13th)
DeAngelo Williams, 1st round (27th)
Reggie Bush, 1st round (2nd)
Mark Ingram, 1st round (28th)
Steven Jackson, 1st round (24th)
Chris Johnson, 1st round (24th)
Darren McFadden, 1st round (4th)
Trent Richardson, 1st round (3rd)
Doug Martin, 1st round (31st)
CJ Spiller, 1st round (9th)
Adrian Peterson, 1st round (7th) ** (Suspended obviously)
Bolded are runningbacks in the top 10, in the NFL, in rushing yards. Italicized are the RB's in the 11-20 range for most rushing yards in the NFL (only nine of them on here because Russel Wilson was in the top 20).