Beyond the task management apps that are now incorporating some form of email management into them (such as Flow, Asana, and even the clipping power within OmniFocus and Things), there are several standalone email apps and add-ons that will better help you manage your email so that you can not only get out of your inbox more efficiently and effectively, but also enjoy the time spent in there.

Keep in mind that these are some of the tools I've looked at personally and feel can work for people. I may be missing some, but it is only because I wasn't a fan of them, or simply haven't tried them yet. I also have not listed pricing here as that can change over time. For more resources, including an up-to-date list of tools that you can use, visit the Email Management page on Workflowing.net. New and useful options will be added to the list regularly.

Postbox

This is my email client of choice. With its ability to integrate with Evernote, its Focus Pane feature, and the fact that it is multi-platform, Postbox is a solid choice for managing your email from the top down.

Drafts

Drafts is where you can prep, refine, and send text for a task called "Email Actions", allowing you the ability to send emails right from inside the app. Using Drafts will also lessen the amount of time you spend inside Mail, which is always a good thing.

Sanebox

I'd like to think of SaneBox as Gmail's Priority Inbox on steroids - but it works for all kinds of email platforms. Because of its algorithm, SaneBox separates your most important emails from the ones that can wait. This allows you to prioritize the way you read your messages, saving you time and frustration.

AwayFind

The idea behind AwayFind's service is to keep you out of your email inbox by having their service send you urgent messages and things that are worth knowing about, while keeping the unimportant messages away. I am a big fan.