Insecure.org publishes Top 100 Network Security and Testing Tools
Only trained IT professionals testing their own networks should use these tools. nmap which was purposely excluded and would be on this list as well. Each tool should be carefully assessed before using them in network penetration tests. Still it's beneficial to test with the some of the same tools that are used by the hacker community to ensure technical defenses are in place at all points.
http://SecTools.Org/
http://www.incidents.org/diary.php?storyid=1438