I've been maintaining the constant_contact gem (can be found here: https://rubygems.org/gems/constant_contact)
It's an ActiveResource wrapper for the Constant Contact API. It works quite well and I'm using it in production.
@someone-from-constant-contact: Maybe you can add this under the "Open Source Libraries" section of http://developer.constantcontact.com/doc/LinksOfInterest, since there are no Ruby libraries there.
Thanks, and I welcome your feedback!