Due to my listening preferences I'm not a big subwoofer guy but they do add some heft and meat on the bones of your music. I don't have to have the lowest depths plumbed so I'm happy with a good eight inch that is both quick and articulate.
I just ordered a SVS Micro 3000 sub. What sold me beside the good reviews is the ability to control the sub with a iPhone app. It also has an auto setup mode using a microphone. You have the ability to save different curves for different sets of speakers and because I'm old and screwed up, I don't have to kneel down or bend over to check settings. All controlled from my listening space. It's also not expensive at $899.