Web Safety Proxy
If you need a complete web filtering proxy solution for your business please take a look at Web Safety - deep content inspection web filtering plugin for Squid running on virtualized infrastructure (VMware vSphere, Microsoft Hyper-V, Microsoft Azure and Amazon AWS).
DNS Safety Filter
For non managed network a filtering DNS forwarder may be a good option. DNS Safety allows you to filter access to domain names by categories, prevent access to specific domains and apply different access policies for different users.