I am using MindManager for Mac. It's quick, it's easy, it's pricey for what it is, and it's a version behind the Windows version. It pretty much does what I need, but it is not very mac-like. I also have tried out Freemind, which is free and more compatible with iPhone mindmap programs, but have not yet spent enough time to see if I will switch to it.
If you have never used mind-mapping software, free is the way to start. I find that my use is mostly brainstorming, to get projects moving, and I transition out of the mind map into an outline/project support format fairly quickly. I don't use mind maps as knowledge maps. I have found that technical ideas don't work all that well in mind maps: they're too long and complicated to be grasped as a gestalt. In that regard, I don't know if Personal Brain is really a mind mapping program. I have only looked at in the most cursory way, but it seems more oriented to knowledge maps. It is perhaps more like Tinderbox, a rather heavy-seeming mac program.