SSL on Multisite with Domain mapping

Hi,
I'm looking for a solution to offer my clients (with their websites on a Multisite instance with domain mapping) a SSL solution. What kind of a SSL certificate do I need and how do I setup SSL for subsites (each with their own domain). Searching through WPML and Google gave me a lot of confusion :wink:

Hope you have a 'step by step' tutorial for me.

Thanks,
Rob Vonk