Cougar Mountain Information
King County Cougar Mountain website
There are two versions of the Cougar Mountain trail map — the black and white map that is part of the brochure that is available at the trailhead, and the more detailed color version.
The Geologic Map of Issaquah shows a great deal about the terrain, and is helpful in understanding the coal beds in Cougar Mountain Park.
The Wikipedia article has much information about the history of the area, as well as a description of the official and unofficial trails.