I've been using TV-Browser for about a month now, with data for the US channels provided by Schedules Direct, the same provider for programs like MacProgramGuide and MyTelly (both of which I've used). Although each program has its strengths, TV-Browser is by far the most configurable, customizable and feature-rich of all three. The list of US channels for my provider, numbers more than 800 channels, which you can configure to the ones you really watch :-)
Its development is active and the developers answer questions, solve problems and constantly add requests from users (they've added two of mine already).
I find myself discovering new features each day and it has become my favorite tv guide application.
Best of all, its open source!