I've always been a fan of mind mapping ideas, and have also used the technique in a team settings during design sessions. But I've never used mind mapping software much. But I just discovered Xmind it is free and easy to use. It has several different diagram types, integrates well with a web browser (internal or external) and even allows me to embed documents inside the map.
So I've started to use it to keep complex world a bit more in order.
I only wish it had RDF capibility so I could name the edges and run SPARQL queries against it.