GIS Data Depot -
provides free GIS data. Includes some boundaries.
Managed Areas Database -
a comprehensive GIS database for the conterminous United States which includes all types of managed areas
(e.g., Wilderness Areas, Indian Reservations, Military Reservations, National & State Parks, National & State Forests).
LandScan -
a worldwide population database compiled on a 30" x 30" latitude/longitude grid,
from the Oak Ridge National Laboratory Global Population Project
GIS File Library -
a compilation of tools and data from Directions Magazine.