The 2011 BAH rates have been released by the Defense Travel Management Office. You will need your duty station zip code and rank to calculate the new rates.
On average BAH rates dropped 0.6% to reflect the recent housing crisis. The rate drop will only affect people who transfer into the area in 2011. Those are currently stationed in the areas that had drops receive rate protection and will continue to draw BAH at the 2010 rate.
You can check out the BAH FAQ page for answers to most of your BAH questions.