Power cables can be the trickiest upgrade of all. Throwing money at a power cable can be a recipe for disaster, if judging by price alone and not hearing with particular components in your system. As power cords can often make the sound better, they can also sound worse than stock cords on certain components.
I currently have a relatively cheap power cord ($200 Harmonic Technology Pro AC 11) on my CD player. I also currently have an expensive ( $2000 Kubala Sosna Elation) power cord on my preamp. Sorry to those who laugh at me, but I can hear the difference. Each cable works well on the respective component, however the $200 Harmonic Tech sounds better on my CD player than the much more expensive Kubala Sosna! I'm happy keeping both where they are (the Kubala Sosna is better on my preamp), but just wanted to share a scenario where more $$$ is not always better for every component. Power cords seem to be component-dependent.
It might be wise to audition cheap power cords, and if you like the sound, buy them. If you like the house sounds of a certain brand on a particular cord, but think you can do a little better, move up the line. But try to determine what sound you wish for, and which power cords might help the most. Different power cables are better at some attributes, while others have different strengths.
Like others in this thread attest, I also believe Audience Power Chord e cables are good power cords. I use them on my mono bloc amps.
