Split testing simply means a straight forward test that compares one version to other. This post contains some powerful WordPress plugins that lets you split test different stuff of your WordPress site.
Title Split Testing for WordPress
As clear from its name, the plugin lets you split test headings to find out which ones attract the most readers.
Google Content Experiments
With this plugin you can use Google Content Experiments on your WordPress site.
SES Theme Split Test
It lets you set up two different templates with differences that you think might increase conversions, serve these different templates up to users, and track their activity using custom segments in Google Analytics.
WP Test Monkey
Using WP Test Monkey you can easily set up multivariate tests on any post or page in just minutes to optimize your headlines, prices, calls to action and more.
MaxA/B
The plugin lets you to create A/B split test experiments using any page, each experiment containing up to 3 variation pages. Metrics are automatically calculated in real-time, and your conversion pages can even be on a different website.