CrazyEgg is a new service that shows a heat map of your web sites, including what people are clicking (banners, links, etc.) and general user activity. It works by installing a script that tracks users and sends the info to your CrazyEgg account.
Plans and pricing
You can choose to have your web site tested for one day, one week, or a whole month, and then a report is generated showing the results. The price starts at $19 per month (and can be as much as $99 per month), but a free version is available which allows you to track the first 5000 visitors in a month.
Why it's useful
It's a good way to get an overview of how users are using your web site and what they are interested in, so that it can be adjusted accordingly.