Guide for Inventors
"How to Protect and Benefit From Your Ideas" from the American Intellectual Property Law Association
Links for Patent Searching
European Patent Office (international)
World Intellectual Property Organization (PCT)
World Intellectual Property Organization (national collections)
Free Patents Online (international)
PriorSmart (international)
IPEXL (international)
Patent Lens (international)
Google Patents (US)
United States Patent and Trademark Office (US)
Japanese Patent Office (including machine translation) (JP)
Delphion - Subscription (international)
Free Patent Downloads (also available from most of the above sites)
Patent Fetcher (international)
pat2pdf (US)
WIPO (PCT)
Other Commerical Services
IP.com: Defensive publications and time-stamped invention archives
Micropatent: Fee-based source for foreign (and US patent documents)
Access to Patent Application Files
MX Legal Client File Portal
Publicly accessible cases in the USPTO PAIR Database