There's quite a lot of software out there for creating mind maps (those diagrams of linked text bubbles). Generally they are great for brainstorming and seeing the big picture before launching into a project. I have used them very little (at least electronically) because the software tends to be feature-rich and cost money, be very very ugly, and make it difficult to synchronise brainstorms between my home laptop and work machine.
I recently came across bubbl.us which I appreciate. It is a free, simple, but well thought-out web application. There is a good real-time help pane, but it is hardly necessary it is so intuitive to use. Since it is web-based there are no issues in failing to sync. I'm not sure if it would meet the needs of power users but for the rest of us it is definitely worth looking at. If you want to keep maps between sessions you will of course have to set up an account. There is also the option to just click and try it without logging on.