Here’s something Google Advertisers will find useful. Google Adwords offers a tool called Website Optimizer. With it, an advertiser can test conversions on different landing pages, headlines and ad copy. It then shows the testing results with graphs to help the advertiser choose the best ad combination for highest conversions.
From the Adwords blog:
help you find out which content will convert best on your site. Whether you define a conversion as a purchase or a newsletter sign-up, Website Optimizer allows you to experiment with different headlines, copy, and images on your site in order to find out which combination results in the most conversions. You can use this tool on your landing page or any page that represents a conversion.
At the end of each experiment, graphical reports show which version of your landing page users liked best, as measured by which variation had the highest conversion rate.
Experimenting with Website Optimizer on your landing page does not affect your Quality Score if you maintain the existing default landing page for the Ad Group.
You can sign up for their beta here.