Most Musical Subwoofers?

I strongly concur with REL as above...I have the Strata III with Vienna Mozarts.
Vandersteen woofers are also highly regarded both in sound and in value.

I guess I have to play devils advocate here and state that the B&W ASW 850 is the best I have heard so far for music and movies. I have it seamlessly integrated in my all tube system and the sub is located on the right side of the right speaker facing towards the same plain across the linear path of both speakers. In all of my measuring and experimentation this is where it sounds best.

Now I am ready to take the plunge and get another one to play around with and see how much better I could make the music experience. But one 15" sub sure does fill my room pretty good already when I need it to jam for rock music, I hate to see how two 15"s will do. For other types of music, the sub is omnipresent without a hint of its existence, except for deep bass energy when I switch off the sub EQ, Velodyne SMS1 and realize that a song had some more energy associated with it, but it is minimal in nature and the sounfield is more alive and vibrant with the sub in action.
Ciao,
Audioquest4life

So I know I want a pair of subs, I'm leaning toward JL Audio, what do you use for a high pass filter, since most subs only come with a low pass filter? From everything I've read, just using a low pass filter and trying to blend the sub with the mains, sounds problematic.

It seems like the Velodyne SMS-1 might be a good choice.
Would I need two for stereo subs? How good is its circuitry? I'll also post this question separatly.

I have not heard the JLs, but I still am amazed by my pair of Vandersteen 2Wq subs. Musical, powerful, and clean bass, and they have blended seemlessly with both Vandersteen mains and my new Ohm Walsh mains. Probably my most satisfying hifi purchase to date.

another vote for the Thiel sub