eqn.me is a nifty little web tool for rendering a LaTeX equation. You type the equation in the box and it quickly renders it as a relatively large PNG. If you need an equation for a presentation or webpage, it’s a nice, quick solution. The downside is that PNG is a raster image; if you enlarge it too much, it’ll be pixelated.
I still prefer LaTeX Equation Editor for OS X by J. McKenzie Alexander, but it’s pretty old. Part of my preference is that it renders to PDF, which you can drag and drop in OS X. It can also be scaled without any pixelation. But like I said, it’s old. I had to install Rosetta to keep using it under Snow Leopard and I can’t find the original webpage anymore either.
I should really take a look at newer tools like LaTeXiT.