forwarded ...
http://slashgeo.org/2011/06/07/Hundreds-Free-Geospatial-PDF-Books-National-Academies-Press
*Hundreds of Free Geospatial PDF Books from the National Academies Press*
Slashdot and The National Academies Press are
offering all their books, over 4,000 of them, for free in pdf format.
With searches, you find plenty of geospatial-related books, for instance:
*Geospatial:*140 books
*GIS:*196 books
*GPS:*218 books
*Remote sensing:*236 books
*Land use:*594 books
*Maps*: 356 books
*Location:*562 books
You can even try more specific terms such as:
*Esri:*53 books, or even ArcGIS: 13 books
*Google Earth:*28 books
*PostGIS:*1 book
*OpenStreetMap:*1 book
It's possible you'll find something related to your own interests in there.