Google Analytics Blog has announced a new Website Optimizer in limited release to AdWords advertisers:
Website Optimizer is a free tool that helps AdWords advertisers test different landing pages and determine which one drives the most conversions. A true multivariate testing tool, Website Optmizer allows you to test variations of headlines, promotional copy, and images. The tool allows you to update your site with the winning test combination and continue to experiment.
The beta launch of Website Optimizer is a limited release that is offered to AdWords advertisers on a sign-up basis. Source
This promises to be a great addition to Google's already robust toolkit for advertisers.