WordPress is known to support like

To embed equations using  precede your code with “latex” and sandwich this with $ as follows [1][2]:

$latex your-latex-code$

To change the size precede the last $ sign with &s=2 like this:

$latex your-latex-code&s=2$

where 2 is the size which could be any number (as far as I know). For example, the Schrödinger equation above is of size 2. It was generated using:

$latex i\hbar\frac{\partial}{\partial t}\left|\Psi(t)\right>=H\left|\Psi(t)\right>&s=2$

Footnotes

[1] LaTeX in WP http://en.blog.wordpress.com/2007/02/17/math-for-the-masses/
[2] WP Support http://en.support.wordpress.com/latex/