I recently wanted to create a mailing list. I was familiar with creating and administering mailing lists on university servers, but that wasn't an option for this mailing list because most of the people on the list wouldn't be affiliated with a university. The obvious choices for free, web-based mailing lists were Yahoo Groups and Google Groups.
Google Groups was more sophisticated than Yahoo Groups, but it doesn't allow you to create a private mailing list that doesn't require members to have Google accounts. If you want to allow non-Google members, you have to make the mailing list public and I didn't think people would appreciate that. I also wanted people to be able to subscribe, unsubscribe, and post to the mailing list via email and not through a web interface. Yahoo Groups fit those requirements. It allows the mailing list administrator to moderate posts and approve new members (if desired). Members also have the option of receiving daily digests instead of individual emails. So, in the end, I went with Yahoo Groups.