There are quite a few of them. Is your focus strictly networking equipment?
Nessus - www.nessus.org (I suspect it's used in business environments every bit as much as the "commercial" tools)
Retina, www.eeye.com
ISS, www.iss.net/find_products/vulnerability_assessment.php
Qualys,www.qualys.com
Foundstone,www.foundstone.com
I'm sure others can prove more as well. If your scanning is more "web" focused, there are tools that are more appropriate (nikto, webinspect, appscan).
