Persistent navigation menus are awesome. I’ve seen them in action on a few websites, like the LDS scripture site and LMT’s website. Not sure what I’m talking about? Go to one of those sites and scroll down. See how the navigation menu pops out and follows you?
The code to make this work is ridiculously simple. Addy Osmani has been kind enough to package it up and release it under a GPL license. As an added bonus, the code includes some nice CSS buttons that you can use anywhere.