I love ; it nicely fills a niche created by my interests in free/open source software, statistics, and design/aesthetics. The results are simply amazing. I've used it for non-technical document typesetting, statistics homework, and typesetting equations.

editors I use:

• Texmaker
• with the Gedit Plugin
• Notepad++ (the PortableApps.com version) is one I bring along to use when on a public computer.

Some other stuff related to that I use:

• The R Project for Statistical Computing + Sweave for statistics
• Tomboy with the plugin for note-taking and personal wiki

Types of equations I've used for:

• General mathematics (algebra, calculus)
• Statistics
• Actuarial formulas
• Economics
• Word equations (like financial ratios)