A combat rogue could buff the burst of your mage by +15% during Tricks, which could be timed with a 9second kidney shot which would give you all 10% extra damage due to Prey on the Weak. In a smokebomb. Sub rogue would offer a bit more CC and sin rogue comes with an execute button, both at the cost of the 9second stuns. Maybe I'm over-rating the stun, but our damage at 90 doesn't look like anything to shout about.
As for what a lock could bring to the team, I haven't played one at 90 so can't comment.