Custom Fields and Post Tags

I am looking for a plugin that would allow me to have a custom field for Post Tags. Any ideas?

Perhaps I don’t need a plugin. Let me know.

I would like to have a custom field in Post Tags to use for a meta description. This might fall under a SEO plugin- I have tried 3 of them but can’t find the right plugin that would allow me to utilize a specific description for a meta description in a Post Tag.

I currently use custom fields to add a meta description for posts and pages.