These are things I’ve tried, and some of them I use a lot.

- ShareLaTeX (thanks, Heather!) https://www.sharelatex.com/
- Online LaTeX Equation Editor (CodeCogs) http://www.codecogs.com/latex/eqneditor.php
- Daum Equation Editor https://chrome.google.com/webstore/detail/daum-equation-editor/dinfmiceliiomokeofbocegmacmagjhe?hl=en
- Math 600 (thanks, Catherine!) http://cemclinux1.math.uwaterloo.ca/~math600/wp/
- LaTeX Support for WordPress http://en.support.wordpress.com/latex/
- JaxEdit http://jaxedit.com/
- MathJax http://www.mathjax.org/
- Latex-MathML Converter http://www.fmath.info/java/latex-mathml-converter/
- Short Math Guide for LaTeX from the AMS ftp://ftp.ams.org/ams/doc/amsmath/short-math-guide.pdf
- LaTeX/Mathematics WikiBook http://en.wikibooks.org/wiki/LaTeX/Mathematics
- Detexify http://detexify.kirelabs.org/classify.html
- MathLex mathematical entry system http://mathlex.org/latex
- JLatexMath http://forge.scilab.org/index.php/p/jlatexmath/

Some other notes that I don’t want to forget:

Use **\(** and **\)** to delimit inline math for MathJax.

Use **\[** and **\]** to delimit blocks of math for MathJax.

Use **\color{***colorname***}{***mathcode***}** to colour chunks of math notation with MathJax.

The format for an equation array is this:

\[ \begin{eqnarray} 2(x + 6) &=& 2(x) + 2(6) \\ &=& 2x + 12 \end{eqnarray} \]