Replacing stock cables: where to start

Good recommendations above. I've had good luck with AZ Tsunami, VH Audio and Virtual Dynamics. Even the entry level Virtual Dynamic PCs I've owned were very good.

Try the Zu Bok or even better the Varial. But the Zu Bok was already better ( much) then my FIM Silver powercord. Buy used, that's much cheaper and they are burned in. I also like the Soundstring and Audience cables.

I'm fussy about my ic's and speaker cables but never found a power cord that sounded any better to me than what you get for $10.00 at Wal-Mart. Your own experience may differ and it is reasonable to assume that it is somewhat dependent upon differences in equipment. A well intended suggestion would be to have some one help you blind test when you start playing with power cords, at the degree of sublety you are dealing with it is easy for psychological factors to overwhelm perception.

Jeff_jones, I found that difference between power cords on a certain component depends on several things. Just to name a few:
1) the overall resolution of the system
2) the quality of power supply in a given component.
3) room acoustics(which also contributes to bullet #1)

also, just how much different a given power cord will sound from a stock cord on a given component also depends on what aftermarket power cord are we talking about.
Example: you will hear bigger improvement over a stock cord with, let's say, a Shunyata Anaconda Helix, than you would by comparing the stock cord to Zu Bok.

Difference between power cords could be as obvious as between interconnects. Things like bass, midrange, instrument separation, air, soundstage, are all affected by cables, including power cords. Also, effect of power cords is cumulative. If you change one, you get certain amount of improvement(with the right cord that is). If you upgrade all, you gain more. Same as with interconnects.
This has been my experience in my system. As we like to say here on the 'gon, YMMV.

Audphile1 - No issues here. I suspect, but don't know, that the reason power cords are not a worthwhile investment to me is your item #2. Most of my equipment has pretty robust filtering, by the time the ac gets all the way to the dc buss it has seen two or three filter networks. If I had equipment designed with sort of the minimalist/purist approach it might well be more sensitive to ac input variance. The other thing that might be hiding power cord effect is that I've got components plugged into line filters, so any gain you get from a cord acting as a bit of a filter network to keep component 1 from creating ac hash for component 2 is probably dealt with in the filter. All that being said, I really do believe that a lot of people would save a lot of money if they would test things in at least a quasi scientific fashion to eliminate hearing what they think they should. Often when you notice that "a veil is lifted and I can hear things I've never heard before" , or some such, it is because you are concentrating more when listening to the new gadget.
Happy Listening!