Dashon Goldson, S
First, the Patriots should focus on the team's 29th ranked pass defense and its not-quite-abysmal, not-quite-talented secondary. Dashon Goldson could fix that up right away. He's a hard-hitting safety that has a knack for making plays on the ball and provides excellent run support.
With 69 tackles, three interceptions and a forced fumble this season, Goldson fits the bill for "talented" and "upgrade."
San Francisco hit Goldson with the franchise tag last season and it will likely do its best to keep him this time around as well. But if he even whiffs the market, he'll command big dollars. The Patriots won't be able to afford him on a short-term deal (they were rebuffed by him last year for the very same reason), but if they wanted to, they could come up with a long-term deal that could entice him.