GIGAOM has put together a nifty article detailing the process for creating a unique iOS home screen icon for your website.
When iOS users visit your website and create a home screen icon shortcut to easily access your site again, you want that icon to stand out and be easily identifiable amongst all the other icons, particularly if your site is a web app.
Normally, when you create a home screen icon for a website, iOS will create a thumbnail image of that webpage, but by following a few simple steps (using a program like Prev