Unless you have a high-end digital source (dedicated DAC), and are worried (anal retentively preoccupied) about getting every bit of digital information to said DAC, as may be warranted in precision critical applications (ie, commercial audio mixing, product testing, or if you have a very high-end/resolving audio system), then any old RCA cable should work fine. Most people don't have equipment that can detect, or themselves can't detect/don't care about, the odd dropped bit for normal A/V applications.
However, the crappier the RCA cable shielding, and the higher the impedance, the shorter the distance it will work over: Any old RCA cable should probably work (unless it's real garbage) for 6-8 feet or less. But if you want to do 20ft runs or more, you might need to invest in something more substantial. I like the
RG6 cables from monoprice. I use them for everything at home from analog interconnects to digital coax to subwoofer cables. If you are/know a cable installer, and can get free RG6 cable, you can simply crimp RCA ends on that to make excellent digital cables...