Depends on the comp.
i usually like running with a boomi for innervate and bres. If not, usually get a fire mage. All of this all depends on what dungeon we are running.
On my resto druid, s.priest, ele, or fire work. BM is nice for weeks with raging or skittish.
The only class I rarely take is locks. Locks do make skips in motherlode easy, but not much else.