I can't remember where I found this, but financial engineering company Sitmo has created a simple, powerful LaTeX Equation Editor that you can use on their website, add to your website or iGoogle homepage.
After writing your equation, you can download it as an image or create a permanent link to it with one click. There's no software to download or messing around with clunky user interfaces (I'm looking at you, Microsoft Equation Editor!).
This is a great example of what Web 2.0 can do for math teachers. Enjoy!