I'm sure I didn't dream it, but I thought I saw a free online tool a few months ago that would display (visually) the link relationships between websites once you enter a URL list.

Failing that does anyone recommend any software like this, paid or unpaid?

Are you talking about the Google enabled visual search?
( http://www.onlineilink.com/demos/google/ )

The search engine Kartoo will suggest relationships. (http://www.kartoo.com)

- Bill

Thanks Bill, you're a star! The onlinelink service was the one that I had in mind :)

Does anyone know of any commercial services such as this?