Take a look at our latest add-on Postmaster. It does a lot more than MC integration. It focusses on providing 1 add-on for all email services. You can create email campaigns just by creating new channel entries. You can create any number of template and variations to have really complex and dynamic interactions. It works with Safecracker and regular Publish entries.
But speaking directly to MC integration, it also has standalone subscribe tags (both a tag and standalone form). You can get any list of subscribers, and even unsubscribe with tags and a standalone form. All of this integration works with both MC and CampaignMonitor with the same tags (same syntax).
https://objectivehtml.com/articles/postmaster-the-definitive-email-solution-for-expressionengine
The next version (v1.2) is finished and currently in beta, which includes support for CartThrob and any other EE hook. For example, you can now send all systems emails with Mandrill or SendGrid. We had a lot of clients complain their receipts (sent from EE using CartThrob) went to spam or they were never received. We solved this problem with Postmaster by redirecting those emails to a proper service (SendGrid in our case) which has a reliable delivery system with reporting and analytics. You can even do things like send an email when a specific member group logs into the site.
We took a radically different approach than all the other add-ons and tried to provide a much more abstract utility that is capable of solving a lot of complex problems. I would have happy to answer any specific questions directly (just use the contact form on my site).