Mail Act-On and MailTags

A pair of extensions for Apple's built in Mail application from InDev software. Act-On allows you to use keyboard shortcuts to redirect your current or selected mail via a set of custom rules. In my case I use it to file away several common general categories of mail, flag them or not based on whether I need to see it again (with a smart folder to view flagged mail), and forward them if needed, all in one easy step.

MailTags stands alone - allowing you to tag your mail much like Google Mail, letting you search for (or create smart folders to find)  mail based on key words that you specify, including useful presets like "Waiting" (for reply). It also allows you to append notes to your mail messages.

Of the two, Act-On is the most useful, and a strong recommendation.