I want to automatically add users to my constant contact mailing list when they register on my site (via oAuth or regular account) How could I do this?

Thank you

It depends where that mailing list is being stored?!

If need be, I can create a temp DB to store new users names & emails then have a different code to add then to the mailing list, from the DB on a schedule.

Basically, when a new user signed up, how can I grab their name and email so that I can use it?

Well you have multiple options. One way would be to modify one of the functions called during the registration for example the RoleMembershipHelper.CreateForumUser which can be found in YAF.Core/UserRoles/RoleMembershipHelper.cs