Andrew Billings, DT
Andrew Billings is the currency on the cap for $3.6M. His deal was so good that the Chicago Bears gave him a two-year $8M extension during the season. The Bears put a lot of resources into the run defense, and it takes a lot to go from 32nd in the NFL against the run to a top-ten unit. Still, Andrew Billings is one of the big reasons that happened.
He plays primarily on run downs, and he plays the nose in most occasions, which does not get much glory, but he has had a huge impact and has helped the development of Edwards against the run.
The fact that the Chicago Bears re-signed him shows that they love the signing, so it is hard to argue against that. It was a great deal, so this gets an A as well.