Inventing on Principle by Bret Victor.
Nathan Yau at Flowing Data writes:
This talk by Bret Victor caught fire a few days ago, but I just got a chance to watch to it in its entirety. It’s worth the one hour. Victor demos some great looking software that connects code to the visual, making the creation process more visceral, and he finishes up with worthwhile thoughts on the invention process.
Think about authoring a graph or topic map with the sort of immediate feedback that Bret demonstrates.