Bergeron and Rask are as close as they come. Rask mostly because it would be near impossible to get a goalie back of his/near his caliber - assuming the team is trading for him since they don't have a decent goalie. If I knew we could get a top 10 NHL goalie back somehow (Price, Quick, healthy Rinne, Bobrovsky, Varlamov) then yeah I'd move Rask for a blockbuster deal. But that is so unlikely he becomes untouchable.
As for Bergeron, it would be a massive, massive overpayment. People saying you don't trade him for Crosby are ridiculous. You trade and you add. Bergy is wonderful, but Crosby is the best player in the world. Imagine Crosby playing with Boston's depth...wow.
Dougie is in the same boat as Bergy since his potential upside is so high and he calms my "Chara is declining" fears.