The only 3rd party apps that are always on in the background are Slacker, Caller id faker, TiKl, and Battery left. None of which are any apps that sync anything in the background.
Check apps like twitter, facebook, etc if you use those. Just press the menu button when you are in the app and then you should see settings. Press settings then you should see syncing options. You can also hit the menu button when you are on the home screen to get to the other settings like gps.