Most of the mock drafts have the Dallas Cowboys taking a cornerback and specifically Nebraska's Alfonzo Dennard. The Cowboys are in desperate for a defensive back, but they are also in need to upgrade an offensive line that is not that good.
Over at Walter Football they have the Cowboys taking an offensive lineman with their first selection:
No. 14 David DeCastro, G, Stanford: The Cowboys have major issues on the interior of their offensive line. Left guard Derrick Dockery is a free agent after missing most of 2011 with a knee injury. Center Phil Costa sucks. Right guard Montrae Holland, meanwhile, can't really be relied upon.
David DeCastro is one of the top interior linemen prospects to come along in years, and he's the highest-ranked prospect on the board. This is a perfect match.