In addition to web hosting, you might offer professional web design, custom templates, installation of scripts and even search engine optimization services. What type of services would you be offering, in addition to hosting?
You've pretty much named them all, as these are the most popular when it comes to add on services. You could choose to offer paid professional webmaster services to your hosting customers which would include a maintenance plan for their website, including regular content updates.
As mentioned before, there are many additional products you can add such as: SSL certificates, backup space, file sharing solutions, domain names or email services.
That being said, they are small volume and in many cases you are reselling some of these features for a low profit margin.
You can also focus on services such as web design, customer support, where you can charge extra to help and take care of putting the site together for your clients to make it more simple and easy on the client as they do not all have web building expirience.