I can't listen to music when I'm actually coding, or during deep design stuff. But at all other times, especially when I'm writing or web surfing, I have a few playlists that I regularly switch between depending on mood. But I spent a long time looking for a visualiser program that could produce nice flowing graphics. My search ended a few days ago. G-Force is spectacular - within 10 minutes of downloading the trial, I purchased the Platinum edition - it was that good. The Platinum edition comes bundled with G-Force Standalone, which produces visualisations from any sound source supported by your computer.
My 3.5 year-old daughter sits on my lap transfixed, almost hypnotised, by the rich tapestry of gorgeous colours and patterns that G-Force produces. Now I just need to hook it up to the 50-inch HD plasma screen, turn off the lights, sit back on the sofa with a pint of vintage Special Reserve Westons cider, and truly chill-out in style.
Disclaimer: I have absolutely no connection with the company or people that produce G-Force, apart from being a happy customer.