Latte

Latte is a Mac OS X application that uses such Web engines as CodeCogs and Google Chart to typeset formulas written in LaTeX.

Formulas can be dragged to other applications (e.g. Keynote, Pages) and, in the case of PDF formulas, scaled to an arbitrary size. Both the LaTeX input and the rendered output can be saved onto your local disk, making it easy to build a library of formulas.