I never thought a power cable could make a difference with a low end system like mine, but then I bought two Tributaries 9 series power cables and all of a sudden my system 'opened' (for lack of a better term). It made no difference to my CDP, but for my amp it was amazing. Retail is $150 ea., but I paid $90 shipped for both.
ICs - I use KnuKonceptz which are cheap and very well constructed, but I can't tell a difference in sound from the DIY cables I made for $4 ea.
Speaker cable - Canare Quadstar. Amazing difference over the DIY cables I was using and the 10awg before that and the Monster before that.