Prefer RealFaviconGenerator
Eduardo Russo was tired of complex favicon creation Show archive.org snapshot and created his own favicon generator Show archive.org snapshot . It's really easy and allows a lot of image editing before rendering the favicons, in all needed sizes, formats and with the HTML needed to include them!
In Rails applications with Haml:
/public
app/views/layouts/_favicon.html
= render 'layouts/favicon'
to <head>
in your application layout(s)... and you're all set.