I know there are several free and paid options out there, but I've read a lot of bad reviews about them not working correctly or needing extra customization to work as designed. I figured since you designed the templates, you would have good insight in designing a comments plugin that works seamlessly with your code.
Just a thought, a comments plugin would be really nice to have. For my site, I would want unregistered users to be able to submit a comment and need my approval before it posts to the live site. The only data I need from the user is their name, email and web address if they have one. The web address should be no-followed for SEO, or maybe you could add an option to exclude it from the comments all together to avoid spam comments.