What speaker cable made a major difference in the sound quality of your speakers??

Used AQ Oaks, that would fit the bill imo.  

Here's some interesting  reading from a few years back. The author knows a little about audio...

Some here, will be familiar with this guy.

http://www.roger-russell.com/wire/wire.htm#conditioner

I find myself somewhere in the middle of cables make a difference augment. Embarrassed to admit that I've spent a couple of bucks on fancy wire. 

If you hear it, and can afford it, what the hell?

Some speakers (most, actually) present complex impedances and are not purely resistive loads (Maggies are nearly purely resistive).

For the former, different speaker cables can make a difference in the sound (and maybe even the SQ).  These cables need NOT be expensive, so use a co. that allows you to try many different ones and return them after a trial.  It is very, very difficult to determine what you need even if you know the impedance vs. freq. plot of your speaker (Stereophile often presents these).  Some co.s (Kimber) publish the inductance per foot or per meter which can help narrow your selections.

Gold plated connections can reduce corrosion.  So can polymeric conductive solutions (one old one was called "Tweek" - ha!).  Break and remake the connections every few years to get rid of corrosion.

Silver doesn't increase SQ (for the record I do have silver cables - they cost me nearly $20).  I also have an old set of Kimber cable used on Vandies, then Maggies, then other Maggies.

The best thing you can do is to run monoblocks with very short speaker cables and long balanced interconnects to the amps.  BUT, this is expensive because you are buying 2 costly transformers.

Each driver would have its own amplifier (designed for the driver's characteristics) in an ideal world.  That costs even more, but as Class D gets better and cheaper we will see a lot more of that.

Bottom Line: Unlike power cables or interconnects, speaker cables (and the cable to the wall wart for your DAC) can alter the sound.  Don't waste money on expensive woo-woo, just use a cable rental co. until you are satisfied.  If you cannot be satisfied, then talk to Mick Jagger.

@jgoomba5  The TWL Speaker cables really are amazing performers. My favorite TWL cable out of the entire loom. The interconnects sound similar to the speaker cables so if you're in need of interconnects and like the TWL speaker cables, you know what to do :P

@sunnyjim I upgraded from the Tellurium Q Black speaker cables to the TWL American Speaker Cables and I could not be happier. Dramatic improvement in my setup. Granted, it is one step up the price bracket as well but I was expecting to feel the law of diminishing returns kick in. Not at all. Worth every penny. As luck would have it, a friend was using the Tellurium Q Ultra Black speaker cables. Brought my TWL Speaker cables over to his place to do a comparison and both of us handily gave TWL the win. The TQ Ultra Black speaker cables tend to lend a darker sound signature but the TWL has better depth, way more micro detail retrieval, a much more natural tonality and a more balanced presentation throughout the frequency spectrum.