InciWeb is an interagency all-risk incident information management system that includes a state-by-state listing of current forest fire activity.
US Wildfire Activity Map includes an interactive map of wildfire locations and various sources of information on past and active forest fires.
National Interagency Fire Center is an excellent site created by the NIFC, which is the nation's support center for wildland firefighting. It features an abundance of information on fires of historic significance.
The Northern Rockies Fire Science Network is a resource for managers and scientists involved in fire management and fuel treatment in the Rocky Mountains.