Whether or not there is a market out there for any of them is a different story. Wallace's contract (3 more years at $10+ million) is practically untradeable. Humphries is on the hook for $12 million this year, but since his contract expires at the end of the season there may be teams interested in acquiring him in order to create future cap space. However, Boston may well choose to hang on to him for the that same reason. Brooks is only getting paid a little under $1.3 million and could draw some minor interest from other clubs, but is also unlikely to bring much back in return.
All has been quite on the trade rumor front for some time now, and most people seem to have accepted that the current roster is the one the C's will head to camp with. But it's possible with new options now at his disposal Danny Ainge may look to make another move.