Best bass response in under $1500 used towers

You really can't go wrong with the Stratus gold is, especiqally used. They're a hell of a speaker

The NHT 3.3's would definitely NOT need a subwoofer.

A bit over your budget, but you may also want to take a listen to the very well-reviewed Gallo Reference III's. I was moderately impressed with them, though not wowed, but I think much of that had to do with the SS amplification in my case. They did exhibit some very tight realistic bass that went plenty low. They offer a sub amp option, though I cannot imagine needing that.

Marco

I don't have a lot of comparisons to go off of, but I would say a used pair of Paradigm 100's would deliver very ample bass.

I third NHT 3.3s (or 2.9s under $1000 used).

Paradigm Studio 100s have 7inch drivers.
NHT 2.9s have 10inch.
3.3s have 12inch. It's not even close in terms of bass response between 3.3s and Studio 100s.

Stratus Goldi towers (with dual 8.5inch?) have alot of output/SPL down to ~40hz....comparable to the 2.9s (which go a little lower).

Here are two detailed reviews on the 3.3s:
http://www.stereophile.com/loudspeakerreviews/1293nht/index.html

Soliloquy 6.3
They have a bass response of 25Hz. Not quite as low as the NHT (22Hz), but something to consider depending upon your choice of amplifiers, and preference in sound.
Good luck in your search!