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 drag'n drop to any application supporting it. This is very useful to insert equations in presentations made with Keynote or Powerpoint. LaTeXiT also features an application service, so that you can type and transform equations directly in most text editors (Pages, Nisus Writer Express, TextEdit...).
Main features of LaTeXiT are :
generated PDFs can be reopened (even with copy/paste) to be modified
syntax colouring and auto-completion of LaTeX keywords
smart LaTeX errors manager
automatic history and library management
included application service
several export formats (PDF, EPS, TIFF, PNG...)