Crazyegg.com provides heat maps, mouse moves, scrolls, corn flakes etc. Google Analytics doens’t provide these functionality. With crazyegg.com you can measure your site usability such as where are your users spending their time and interacting with your site, where are they clicking or scrolling to which is quite valuable information.
Alternative to crazyegg.com there is hotjar.com which also provides heat maps, conversion funnels, visitor recordings on different devices.
Optimizely.com optimizes web experience via A/B testing. I worked on the similar project at ebay.com and certainly it has great benefits. You can set up tests for small percents (%1 or %2) of your site users to view different view of your site. You can measure and optimize your usability with the results. You can optimize your site, campains and increase conversion.
Browserstack.com helps you automate tests of your site for different browsers easily. It provides a device cloud for testing your site. Broserstack can also generate screenshots for different browsers running on different devices.
Pingdom tools helps your measure your site speed and with optimizations you can make. This tool shows your site performance with respect to DNS lookups, round trip times, size of site’s media etc.