There are 3 main tools that you can use. Optimizely, Visual Website Optimizer and Convert.com. Convert.com is much less known but it's also a great product. They are all roughly the same price with minor feature differences
I've been using Visual Website Optimizer since 2011. It's great for newcomers has much improved usability recently and for new users, it's extremely easy to launch your first test or campaign.
Their blog is also packed with case studies. The convert.com blog is also great for best practices and things to remember/consider before split testing.