This is Navixia's list of Links and Tools related to Security.

Security Tests 

Test your DNS configuration  http://www.dnsstuff.com/
Test your proxy configuration http://www.eicar.org/anti_virus_test_file.htm or http://www.lagado.com/tools

Security Tools 

Free SSH client for windows  Putty
Free SCP client for windows  Winscp or FileZilla
Free sniffer for windows Wireshark
Free LDAP browser Softerra
SIP Security Scanner Sivius
Microsoft Baseline Security Analyser MBSA 
Sysinternal PsTools

Security Links

Sign and Secure your email traffic. Navixia partners are Web of Trust Notaries and can give you points.

Google Hack http://johnny.ihackstuff.com/
Voice over IP Security http://hhi.corecom.com/voipsecurity.htm
Find vulnerabilities for your devices in CVE database http://www.cve.mitre.org/cve/