I was an early adopter of both Magic Action Box and Wysija newsletter plugin.
MAB and their support are both totally fabulous. If you think the 'out of the box' styles are terrific then wait til you start playing around with making your own personalized boxes - that takes optins and click thrus to a new level.
This is a very much recommended plugin, even if you just use the Lite version. Go grab it and try it out for yourself.