. Google Website Optimizer

Google now offers a gratis testing and site-page optimization tool. After some intelligent planning (Google suggests places to get started) and selecting page design (either multivariate or a simple A/B setup), you can be well on your way to testing landing pages or regular site pages.
Here are a couple of benefits of using Website Optimizer:

• Projections of time to completion of tests and other aids mean that you don't have to be a statistician to pursue the advanced testing.
• The reporting is powerful. Both the reporting and the rotation functions work on their own, without any special, clever effort from the user.