How do I get the domain of a site within a multisite network?

I'm writing a plugin for a MS install. Within that plugin I want to be able to get the domain name of a given site the plugin is running under.

I'm not super familiar with MS so I'm not sure how domain mapping and any other MS magic might effect my ability to get an accurate and consistent value for the current site.

Or perhaps I'm better off using the site ID? I would prefer not to use the site ID since 1 or 2 or 3 isn't as recognizable as,, or some other word based name / label.

Make sense?

Thanks again.