I've just uploaded a new extension to the ExpressionEngine forums which may be of interest to you.
You can read the full details here, but in brief the extension will automatically subscribe newly registered users on your EE-powered site to the MailBuild or CampaignMonitor mailing list(s) of your choosing.
I hope you find it useful.
Awesome work Stephen, thanks so much for putting that together. Loads of our customers use EE (including us), so I'm sure this will be popular!
Just a quick note to say that I've released a new version of the EE extension, which now allows users to opt-in to (or out of) the mailing list at the point of registration.
Great update Stephen, ad nice work on the screencast too.
As a web developer using expressionengine for all my clients now, this is terrific news!
Adding the fact CM is one of few if any newsletter systems where one can import right from your site a separate area made for a newsletter, this makes CM #1 choice.
Blog a campaign!