MathType is a powerful interactive equation editor for Windows and Macintosh that lets you create mathematical notation for word processing, web pages, desktop publishing, presentations, elearning, and for TeX, LaTeX, and MathML documents.
KLatexFormula is an easy-to-use graphical application for generating images (that you can drag and drop, copy and paste or save to disk) from LaTeX equations. It is written in Qt4.
LaTeXiT is a small utility that allows you to quickly typeset LaTeX equations, without bothering with file creation, preambles, and so on. The PDF image obtained can then be exported by dragn drop to any application supporting it.