Millwood's the right pick to swap for a decent closer.
Santana's the real deal, but still working back from elbow surgery, so moving him and Lieber for five months of Prior would be about right. If that deal doesn't happen, dump Lieber for Carpenter. I would't take Garland over any of your guys.
Affeldt and Lee are big upside guys, and, as noted earlier, Hampton finished strong last year and seems to have recovered from the Coors disaster. Overall, your staff seems OK (particularly if you get that second closer).