United States Patent and Trademark Office (USPTO)
Search http://patft.uspto.gov/
General http://www.uspto.gov/web/offices/pac/doc/general/

Other government patent offices
European EPO http://www.european-patent-office.org/
Israel http://www.justice.gov.il/MOJEng/RashamPatentim/
World (PCT WIPO) http://www.wipo.int

International search sites
WIPO http://www.wipo.int/pctdb/en/index.jsp
EPO http://ep.espacenet.com/

Non-governmental patent information sites
www.yahoo.com/Government/Law/Intellectual_Property
www.ipmall.fplc.edu

PDF copies US pats www.pat2pdf.org