One thing that always annoyed me about Cool Edit Pro (now Adobe Audition which seems to be much more annoying to use in several respects) is the quality of the waveform visualization. What it seems to do is find the highest and lowest signals at each horizontal pixel and draw a vertical line between them (interpolating as necessary if you're zoomed way in). That means that when you're zoomed, the waveform is a big blob of green with very little useful detail in it. Only green and black pixels are used - no intermediate colours are used to smooth the image. Other waveform editors I've tried seem to work in similar ways.
I think we should be able to do much better. Suppose we rendered the waveform at at an extremely high resolution (one pixel per sample horizontally or better) and then downsampled it to our window size. There's a problem with doing it that way, though - unless the waveform only covers a few pixels vertically, the waveform is going to be spread out amongst too many pixels and will be very dark. Imagine an analog oscilloscope with the beam intensity set at normal for a horizontal trace and then visualizing a signal which oscillates over the entire display at high frequency - most of the signal will be invisible with the exception of the peaks.
The solution to this with the analog oscilloscope is to increase the beam intensity. We can do exactly the same thing with a digital visualizer too - we're not limited to 100% intensity for our intermediate calculations (if a pixel ends up at more than 100% in the final image, we can clamp it or use an exposure function). Increasing the intensity to infinity gives us the Cool Edit Pro visualization again - the any pixel the waveform passes through is fully lit.
What does it look like? Watch this space to find out!
Edit 14th July 2013: