CrazyEgg is a popular choice because it allows you to throw a little snippet of code in your site and it will track where every click is going and where the mouse pointer seems to be positioned by the users.

This is great for doing split tests of your site, and to show investors how your traffic is being handled.

TIP: If you sign up to their site, give it a day and then CANCEL it. What they'll do is come back to you with a counter offer for a full year at a really low price. If you like this service and you have a website that needs heatmap tracking, I recommend this.