The best speaker you ever heard?

In my opinion, the speaker is by far the most important part of the audio system. After all, it is the only part you hear. OK, the other stuff really matters a lot, but without a great speaker... No go.

I am a bit 'speaker-obsessed' I guess, and now I am wondering: What are the best speakers you have ever heard, and what made them the best?
The Quatro's arrived and are breaking in nicely.  Loving the sound.  Just amazing all around speakers.  They are set into the corners right near the wall. The bass and size of the soundstage is amazing.  Best speakers I've had in the house.  Probably, for me, the best buy in high end audio IRT speakers.  The sweet spot in Vandersteen's line.
Personally, I love Megaboom 3 and JBL Xtreme 2. They're both solid and stylish speakers. Of course, UE's speaker is definitely superior, but Xtreme 2 seems to be nice too. I'd recommend Review Position if you're planning to do research and head-to-head comparisons. They're really good and know what's what.