From the DOS website:
Effective April 13, 2012, the Department of State will adjust visa processing fees. The fees for most nonimmigrant visa applications and Border Crossing Cards will increase, while all immigrant visa processing fees will decrease.
The Department is required to recover, as far as possible, the cost of processing visas through the collection of application fees. For a number of reasons, the current fees no longer cover the actual cost of processing nonimmigrant visas. The nonimmigrant visa fee increase will support the addition and expansion of overseas facilities, as well as additional staffing required to meet increased visa demand.
Although most categories of nonimmigrant visa processing fees will increase, the fee for E visas (treaty-traders and treaty-investors) and K visas (for fiancé(e)s of U.S. citizens) will decrease.
For a full list of the revised fees, see the full article on the DOS website here.