The University of California Press now has over 2000 e-books published between 1982 and 2004 available on their web site. Over 500 of the these are freely available for full text public access. Topics covered include sociology, politics, art, science, history, music, religion and fiction. Search as normal using the Advanced Search and then limit your search results under the SHOW tag to public access books. Have a browse at
http://publishing.cdlib.org/ucpressebooks/