Me myself, I'd have to say the top four offensive d-men in the league over the past five years have been Pronger, Neidermeyer, Lidstrom and Gonchar. I'm too lazy to check the stats but I'm about 80% sure that Gonchar has the most goals out of the four in the past couple of seasons.
Sure he's no gem in his own end, but he's not as Horrible as he's portrayed in the forums.
As for who we'd give up, I'd say Bergeron and possibly Pouliout(sp?). I think that the Pens would jump for a chance to reunite Crosby with one of his old linemates.