Firefox: GTDInbox is a Gmail add-on that converts emails with requests, projects, or follow-ups into do-able actions, while still keeping your inbox clean. It's updated since we last looked, and keeps up to date with Gmail's changes.
GTDInbox still pulls off the same kind of functional archiving as it did from its first version. Emails being written, replied to, or stashed can be labelled as To-Do, Waiting On, Some Day, Projects, or other labels you add in. The add-on, however, also works with, and tweaks, some of Gmail's own features, like disabling the auto-hiding of all but the most recent labels in the left-hand sidebar, allowing for message previews on hovering, and labelling emails as you write them. You also get another compose option that allows you to quickly write a note to yourself, without having to address it.
There's a good deal more in GTDInbox to discover. It's a free add-on (with a Premium edition with additional features available), works wherever Firefox does. It seems to work well with Better Gmail 2 and other Gmail extensions, just not those with label-modifying powers. It also has a small issue with some Linux systems, which can be overcome with some manual tweaking.