Look at these:
They are all produced by LaTeX. LaTeX is a publishing tool which is very fit for people to handle articles which contain a lot of math formula. But LaTeX produces DVI or PDF files, instead of images. So they can not be insert into a web page directly. Furtunately, there is a free software, mimeTeX, a CGI program, can produce image files through LaTeX strings. It runs at server, so it can provide images for any web pages.
Even better, there is a free public mimeTeX service, www.forkosh.dreamhost.com. If you want to add some formula to web, just use <img src="http://www.forkosh.dreamhost.com/mimetex.cgi?Your LaTeX text" />. You can use this method to add any math formula to any website.