Freemind, but have transitioned to x-mind.

RegEx Coach

Most of Red-Gate's stuff

Innovasys DocumentX.

Notepad+

I used to enjoy acquiring tools and get excited over the new features but then I found that I was spending more time on an endless cycle of learning new tools rather than actually using them productively. I was fooling myself that I was doing productive work when in reality I was playing with something.

At most the new tool would give a single digit boost in productivity but chances are what you gain on the swings you lose on the round-a-bouts.

I find now that I ask if the tool is actually addressing a major pain point rather than an itch or a tingle.