I heard from a somewhat reliable source that the following is the intended release schedule for WFB over the next year or two. I've had it corroborated by one of Warseers rumourmongers who sthall remain anonymous unless he choosed to post here:
Ogre Kingdoms (2011)
Bretonnians (2011/12)
Wood Elves (2011/12)
Dwarves (2012)
Lizardmen (2012/13)
With Wood Elves and Bretonnians in uncertain order.
Bear in mind these are rumours, and even if accurate these things are subject to change.