I'd like to throw out the name Byron Marshal as an udfa for a third down back. He started his career as a rb so he has experience with blocking and running out of the backfield. He was moved to wr because of the rb depth and he became the most reliable receiver almost immediately. He has great hands and is a dynamic runner after the catch. He's been ranked as going undrafted so it wouldn't cost a pick and I don't think he'll make it as a wr. I think he'd make a great weapon in that position, especially now that everyone says we're a pass oriented offense.