As our servers run cPanel, the main web server is apache. Apache is great for PHP (it is the fastest one to return PHP content), but when it comes to static content (images, html, javascripts) it lacks performance.
We have added nginx to our web servers, which acts as a reverse proxy and returns all static content instead of apache.
This lead to a huge performance increase, especially on sites with lots of static content (for example image galleries, html only websites, websites built with website builder). We have noticed reduced page loading times, sometimes even by 4 times.
We are also working on optimizing mysql service, which will reduce query execution time and will lead to performance increase on database sites.