[DJGeorgeT]

Super.Fi 5 EB has practically a subwoofer with its dedicated dynamic driver that only handles the bass through a crossover.

 

[nonsupremous]

What about the Q40?  I have never personally heard them, but have heard and read that they can deliver quite the punch. 
 
Also, if you really want a subwoofer with a headphone, Skull Candy actually makes a headphone with a battery powered mini sub connected to the cable.  I can tell you that the sound is not really great (one of my kids has a pair) but they will deliver some serious head rattling bass!!  I'm pretty sure we paid somewhere around 60 bucks at Best Buy for them. 

 

[nickweed]

I had some Equation Audio's that were awesome with getting that bass across without totally overwhelming everything else within the music. They were they Dj styled ones, silver in color.  I gave them to my brother so I forget the exact model.