I'm looking for a standalone math equation renderer that generates a gif or png file. It should be able to take equation input from a URL. It has to work on a webserver, preferably on IIS and .NET based.
I read the previous topics here, but none of them seem to work well.
Latex2PNG does the trick. Moreover, its source is very simple (< 100 lines), so you can easily see how to build one yourself. If you want to build such a thing on a Microsoft stack, you'll need to install latex on Windows (not too hard), or write some code to dispatch the render requests to a unix machine with latex.
I know this doesn't directly answer your question, but most people don't think about this first time, so you might want to consider it.
You can render the LaTeX client-side with javascript libraries such as jsMath, it is nice because it introduces no overhead to your server, and can be dynamically edited.
tex4ht renders all math as gifs. it comes with miktex. you can use it from the command line. it will also dump to math ML.
You can use some web-services that do this, like MimeTeX or MathRan.
See also this.