When I had to write some formulas in the blog I used to render them from LaTeX to images using some websites such as Online LaTeX Equation Editor. It has the disadvantage that you've got to write the equation, render it, save it to your harddisk and then upload to the WordPress file manager. Now, thanks to an interesting plugin written by Steve Mayer you can embed its usage into WordPress just by typing the LaTeX commands between special tags.
It uses MimeTeX which is an standalone program that directly renders LaTeX expressions into images without using the entire TeX package or its fonts. Thus, it's a simple, lightweight and elegant solution ready to be used in your websites or blogs.