Ivan Lopez has released a new commercial WordPress plugin called AB Press Optimizer that's aiming to be the de facto WordPress A/B testing solution. If you've never experimented with A/B testing, you're missing out. I've seen results from theme and plugin sellers that are staggering, based on relatively small changes. There are some pretty good non-WP A/B testing tools, like Optimizely and Visual Website Optimizer, but if you want to keep your tests within the WordPress admin, AB Press Optimizer might be the ticket. Pricing starts at $39.