What is the oldest version of Solaris that Sun will still support?

I am working within a group that is trying to define recommended
standards for Operating Systems that our organization will allow to be
deployed. We would like to list the lowest version of Solaris for
which Sun is actively providing current patches, updates and support.

We will probably list Solaris 10 as the standard version to choose and
Solaris 9 as a declining version and Solaris X and below, where X is
unknown (maybe 8), as a version to discontinue use of.

What are your recommendations?