Some of free tools that help you doing the regular inspection work for our web applications for potential vulnerabilities:
NT Objectives' NTOinsight and NTOweb from http://www.ntojectives.com/freeware
ScreamingCobra from http://samy.pl/scobra
Massive Enumeration Tool from www.gnucitizen.org
Foundstone's SiteDigger from http://foundstone.com/resources/s3i_tools.htm