I tend to keep going back to the listings on
Yahoo! TV, since I can personalize it with just a zipcode, and bring up either a fairly generic listing or a specific group of channels based on actual cable companies in the area. You can also list only the channels that interest you, which I find very useful.
I've stuck with them for a good while, since their listings seem less cluttered than most of the online ones.
(used to love one called TVGrid, but it bit the dust a few years ago.)