I have owned or demo'd a lot of interconnects and power corrds in both my headphone and speaker rigs. The best sounding interconnects I have used are Crimson Music Links. Austin Hi Fi sends out demos and they are not ridiculously expensive. The second best were WyWires, which are more expensive than the Crimson Music Links. If you want something cheaper, Clear Day Cables interconnects are quite good for the money (~$150). I have owned Purist Audio Design, Tara Labs, Gabriel Gold, Cardas -- none were nearly as good as the Crimsons.
The best power cords I have owned are Mojo Audio Enigmas. I also own a few Triode Wire Labs cords, which are somewhat warmer sounding but don't sound as extended as the Mojo cords. (Overall, I have found that power cords make a bigger difference to sound quality per dollar spent than interconnects, where differences between good and great are usually fairly subtle.)
Hands down, the best speaker cable I have owned are the Clear Day Cables Double Shotguns. The owner of Clear Day, Paul Laudati, is a really great guy who lends out his cables without even taking a credit card or deposit from customers.