[CentOS] Recommendation for a Good Vulnerability Scanning Service?

Hi,

Can someone recommend a good vulnerability scanning service? I just need the minimum for PCI compliance (it's a sort of credit card processing certification).

I got a free scan from https://www.hackerguardian.com/ and their scan reported a number of "Fail" results. I haven't checked them all yet but most seem to be things for which fixes were backported looong ago by The Upstream Vendor.

I haven't spoken with the hackerguardian people yet but it would be nice if I could just say "I'm using CentOS 5.5" and have them factor that into their report so that I can focus on any real issues. Are there vulnerability scanning services that are more or less sophisticated about this?

Thanks, Mike