Best subwoofer to complement my system.

Actually, I don't think it's very difficult to implement a subwoofer into a system but it takes a little planning, experimentation with the sub placement, room size, and dialing in the proper configuration for crossover, volume, etc..

Perhaps most important is a little known secret about syncing up a subwoofer to the main speakers. Some to many interconnects and speaker cables (regardless of price) induce time smear to a small or large degree.

Of course the ideal is to acquire ics and scs that induce little or no time smear. To minimize any disjointedness between the main speakers and the subwoofer, it is imperative that the ics and scs apply similar design methodologies.

For example, if the interconnects to the subwoofer induce much time smear but the speaker cables to the main speaker minimize this time smear, the subwoofer will sound syrupy, wooly, ill-defined, slow, etc. whereas the main speakers' bass will be tight, fast, full, well-defined, controlled, etc.. And there is little or nothing that can be done to remove this disjointedness regardless of tuning, tweaking, and placement strategies you apply.

But when I say it's not difficult, every situation and every room is different, and every sub and speaker match is unique. But there are certainly several things you can apply that will minimize your grief.

-IMO

I am also considering the same thing though not sure yet. Apart from the companies mentioned above, you may want to check out Thiel's smart sub.

Thanks for all who responded. Bottom line is I need to do some more research!

Velodyne make the SMS-1 to help integrate a subwoofer [or subwoofers] into a system. I don't own one, but I am intrigued and would really like to try one sometime.

The real key to easier sub integration is either using a speaker with bass which runs to only around 60hz,or using a high pass crossover on your speakers to cut off bass below this level.I'm not saying this will help in every situation but it is a general truth and one which is rarely seen in domestic speakers but common in pro systems.
This seems to be especially true for electrostats or panels.
Also I have found that large coned down firing subs positioned between the listener and the speakers[coffee table style] often work better than forward firing in the line of or near the speakers.