I'm not really familiar with the exact classes that sit at the top of the DPS meters right now but I guess that really varies from case to case and who you run with. I know Death Knights are up there and i guess Ret Pallies, Warlocks, and Mages are also frequent chart toppers. But it seems like certain specs of certain classes aren't doing so well in their dps output and Blizzard has taken notice. Blizzard is currently monitoring how the classes are doing so that they can potentially make some changes to help boost the output of those they feel need to be buffed.
Patch 3.08 saw some changes to the Elemental Shaman tree that gave them a pretty big dps boost. Ghostcrawler already mentioned in the official forums that they're going to take a look at Combat Rogues, Kitty Feral Druids and Beast Mastery Hunters as the specs that they feel might need a boost. I think the buffing of Elemental Shammies shows that Blizzard does listen to feedback and adjust accordingly if they feel that's what's needed. It might take some time but they get it done.