Ok, I'm going to stay away from a fantasy "wish list" and will avoid those i think have a very very slim chance of being moved.
Top of my list is Stastny ,
but it comes with 1 unmovable condition, Komi has to be part of the package going back. Stastny is not even close to earning his pay check there and we have no guaranties he will here either. We must drop 1 albatross contract before we risk taking another.
The safest and very possible name to fit in the middle of those 2 for me is
Patrice Bergeron is a 1b/2a center. He isn't a bonified #1 and if you run into a playoff series against Crosby/Malkin/Staal and Bergeron is your best...you're still screwed.
Kessel and Lupul are shooters. You need a playmaker for shooters. At this point they are setting each other up because the center that has been played on that line has been less than adequate. If you give them a player that can dish the puck people stop hoping Kessel scores 40 and start expecting it season in season out because he finally has a legitimate middle-man that can feed him in the tough areas.
Patrice Bergeron is a great 2 way Center, he plays all three zones, he back-checks, wins 65 - 70% of faceoffs, he 15 Goals 28 Assist and has a +/- +27. the only reason Bergeron is on Bostons second line is the chemistry between Boston 1st line Lucic, Kregci, Horton, and they don't want to break up the chemistry between Seguin Bergeron
Kessel and Lupul can fly down the rush and make high skill plays already, I think the biggest need for a center is big guy who can cycle well. When teams neutralize our speed (which is happening more and more regularly) we need to rely on the cycle to put up points which Kessel and Lupul arent especially good at. A center who can crash and bang be good defensively is what we need.
Now that I think about it I really think Grabo should get an extra look as our 1st line centre, I know weve tried him before, but his 2way play, board play and ability to keep up with Kess/Loops could work well. Last year he showed he's capable of being a top line guy.