I am willing to consider trading Longoria, Mauer, Domonic Brown, Josh Donaldson and maybe Kimbrel.
Right now, as you've seen in my posted keepers, Mauer is odd man out, but he barely lost out to Donaldson, Brown and Kimbrel (all four are close). He has the best OBP for catchers and since he plays 1B/DH he generally accumulates more games played than your standard devoted catcher (assuming health).
Mauer can be attained with a pick upgrade. Longoria will require a player of equal value (not necessarily a pick upgrade needed to trade Longoria). The others I'll just have to see about if there is interest, but Kimbrel and Donaldson will likely be difficult to pry from me, but I'm open to offers and be convinced otherwise.