I thought that an adjective used to describe something that stimulates was "stimulating."
As in a "stimulating conversation" or "that jump in the lake was so stimulating!"
But with respect to the Economic Recovery and Reinvestment Act, commentators wonder and debate about whether various parts of the bill will be "stimulative."
I guess that is the proper way to describe something that stimulates.
Besides, talking about whether the package will be stimulating sounds vaguely perverse.