All about the bass

The speaker I heard with the tightest and fastest bass and within your price range is the Audio Physic Avanti III. I think it costs about $10k new but you should be able to find a used pair for under $5k since the revision V is out.

BTW, it does need a high power amp to come alive.

Better option, Def Tech Mythos ST's, <$4K/pair new.

Very efficient with bass down to 14 Hz via a powered sub in each tower. I had them in my rig and was pushing 110 dB peaks with bass to shake the room,

Generally a great sounding speaker to boot, you'd have to spend multiple times that amount to get similar response.

Lilu:

Very good topic and one where you should get a split in opinions. This is just my view: the benefit of using a sub woofer is that you can regulate your bass extension from one CD to the next by simply adjusting the settings on the back of the unit. This gives you I believe more flexibility than if you just had a large pair of speakers and just a bass control on your amp/receiver. It's simply amazing from one CD to the next how much I end up walking over to my sub woofer and adjusting it. For example, if I'm playing a CD by Four Play or Brian Culbertson (jazz), I have to turn the sub almost off. What size is your room and does it have thick carpet and much upholstered furniture? Is it on a first floor slab or wooden floor? In the $3K area, look at Rotel, NAD, Marantz, for integrateds. Is this to be a two channel system or home theater set up?

The SP Timepiece mini
http://www.audiocircle.com/circles/index.php?topic=48306.0
http://www.audiocircle.com/circles/index.php?topic=48470.0

Athough the smaller brothers of the Timepieces they are very similar:
http://www.positive-feedback.com/Issue30/sptech_2.htm
'These speakers are among a handful of speakers that literally define the concept of "value" in the high-end audio price/performance ratio. Today that ratio needs supercomputing assistance to unravel hyperbole from fact. When I listen to my Timepiece 2.1 speakers, I am the sound of one hand laughing because, these speakers are among the best I've ever heard at any price.'

At $2995 cheaper than your 5k limit. Put the difference into better source components - the SP's deserve it.

The amps I recommend are the D100's from channel island audio if the new digital amps take your fancy:
http://www.audiocircle.com/circles/index.php?topic=48465.0

But for untimate performance you really can't go past the Hugh Dean Soraya:
http://www.aksaonline.com/buying/buying_price.html
http://www.diyaudio.com/forums/showthread/t-108756.html

Not the most expensive amps about - but simply the best.

For source I recommend computer audio from a modded Squeezebox. The ultimate in convienience, and now sound quality:
http://www.audiocircle.com/circles/index.php?topic=42526.0
http://www.audiocircle.com/circles/index.php?topic=38027.0

The above is not the most expensive system on the planet, but is certain to be amongst the best.

Thanks
Bill

Because you have a small/medium sized room, I would recommend spending only $3k on speakers and budgeting $2k on room treatment (Realtraps or GIK), as bass performance is often dominated by room acoustics in a small room. Maybe not the answer you expected, but probably the best one for bass performance.