The idea behind CrazyEgg is simple – show the hotspots where users click on in a site. This information is not the same as popular pages; instead this is practical information about how and where people click on your site. More importantly, CrazyEgg’s approach lets you understand the difference between where you want your users to click and where they are actually clicking.
Here is a heatmap of my photoblog at www.dirkpaessler.com (click the image to zoom in):
CrazyEgg also adds tons of other user tracking features. A trial account with up to 50.000 visits is free.
Via ReadWriteWeb (they also also have a longer description in their site….)