PFF has John Abraham as the most productive edge rusher in the NFL over the past 3 seasons. Charles Johnson is 8th, Ray Edwards is 11th (ahead of Jared Allen for those who say he is only good because of Allen).
Meanwhile Jamaal Anderson is the 2nd least productive edge rusher over the last 3 years, and Chauncey Davis is the 10th least productive. Obviously Edwards or Johnson would really improve our pass rush.
Pass rushing productivity measures sacks, hits and hurries out of total pass rushing snaps, so is more valuable than just looking at sacks. Perhaps Ray Edwards is a bit underrated on this board looking at these lists.