If there is one diy project you want to try, it's cables. It's a fairly quick and easy project, you save a great deal and you get the exact length you need.
Here I'm assembling a resource on speaker cables. It's currently a work in progress.
Do speaker cables make a difference?
Absolutely. It's very hard to make sound without them!
Firstly, let's keep things in perspective. In an entry level system, cheap figure of 8 cables for a few dollars per metre are adequate. The cables will never be the weak link. In a higher end system, it's worth getting a bit more serious, but even there I'm not suggesting to spend thousands.
Snake oil free zone
Differences in speaker cables are subtle and they are based on measurable differences. There are some with vested interests that want you to believe that differences can't be measured or quantified. That way they can convince you that their cable is better, even though it doesn't measure better. Others quietly consider themselves part of the audiophile elite - those with golden ears who are above science. They are a cut above the rest of us!
Things that matter
The main properties of a cable are L, R and C - inductance, resistance and capacitance. Capacitance is generally of little consequence to sound quality. We can compromise most in this area. Resistance - we'd prefer to keep it as low as possible, as it will result in losses. Thicker cables tend to have lower resistance, but bigger isn't necessarily better. Longer cables tend to need to be thicker. Inductance - we'd prefer to keep this also as low as possible.
Cables and Safety
Certain cables can't be used with certain amplifiers. High end cables tend to reduce resistance and inductance, but have higher capacitance. This is a problem for Naim and Linn amplifiers that eschew load stabilisation networks. Some caution is needed. If in doubt you should check the manual of your amplifier and check with your retailer.
A low cost high performance DIY solution
Credit for this goes to Trevor (aka Zaphod Beeblebrox at the StereoNET forum). High power coax RG213/U makes a very good low cost speaker cable. Apparently it is better than most pricey boutique speaker cables. The exceptions are expensive and offer a very small improvement.
Why is it so good? It's designed for high frequency use with low loss. That means very low inductance. The cost is around $4/m for small amounts.
How to use it
One coax will do for a passive speaker. The centre conductor carries + and the shield -. You will need to strip back the insulation and solder in lead out wires at each end - one to the centre, the other to the shield. Heatshrink tubing will neaten up the cable.