I recently installed boomerang for my gmail account. It has some promising features, below you can read what you get, the description is copied from the boomerang website http://boomerangapp.com/

What Boomerang is about

Today, Boomerang helps its customers focus on email that matters, when it matters. Our tools allow for reading and responding to messages faster and more decisively than before. These achievements mark only a small part of how we envision the company growing.

Our mission is to make productivity software that encourages people to be more productive. Some of the beliefs that will guide us as we work toward this mission include:

Context-aware. The next revolution in productivity software will come from software that analyzes the context of what we are working on and adds value on top of it. Leading the shift will require technical skills that few teams have. Fortunately, we have these skills, and cloning the functionality will remain difficult for years to come.
Sensible defaults. Context-aware systems will not be perfect, and spending time trying to make them so is a task for academic researchers. Instead, the system needs to supply an easy way for users to change mistakes, without imposing too heavy a burden on them. Designing this interaction properly will be a major challenge, which our team is well suited to conquer.
Persuasive Software. Research in practical psychology continues to uncover surprising truths about how our minds work. Our productivity software will incorporate the results of that research into broad, horizontal products. Designing these interactions will require significant skill and discretion, as we have learned from The Email Game.
Communication first. Applying our core productivity themes to communication and collaboration software will result in the greatest impact. We will not make the mistake of trying to build a competitor to all of Microsoft Office in one fell swoop, and we will likely never make a spreadsheet.
Data-Driven. We believe that data is the closest approximation to the truth. We will base our decisions, wherever possible, on the results of statistically-significant measured data.
Respectful software. We will not make software that helps one party profit at the expense of another. There is a fundamental conflict in the email space. Some companies seek to profit by increasing the effectiveness and intrusiveness of gray email, to the detriment of our privacy and our ability to choose how we spend our attention. We seek to profit by increasing the effectiveness of everyone else.