When was the last time you checked out TouchGraph? It's been at least a couple of years for me, but I ran across it again while Stumbling. Wow, either I don't remember it being so cool (although I do remember it being cool), or it's evolved nicely since then. Here's a screenshot of one of my site's neighborhoods. There's lots of slider controls, filters, and other gizmos that let you adjust things.
If you aren't familiar with TouchGraph, their description of it is:
The TouchGraph Google Browser reveals the network of connectivity between websites, as reported by Google's database of related sites.
This is what I'd call the Cool SEO tool of the day (even if it has been around a long time).