640kg this year.
However the weight limit is due to rise, i belive it will go to 650kg for 2013 and then stay at that for 2014 and there after.
Personally id like to see refueling back with the cars being 650kg so they can run larger KERS batteries for more boost from KERS, or instead of 6.6 seconds a lap, raise it to 15 seconds a lap. As for refueling, make it that the fuel stop has to be seprate from tires and done via two 22kg bottles simmilar to what they had in GT racing and what they have in NASCAR, like this:
http://www.chicane23store.com/index.php ... s_id=13636
Id also make it that each car has to have a spec 90kg fuel cell that has to be filled with at least 70kg of fuel for leaving the pit lane for the reconasance lap to the grid.