According to the 2007 Internet Filter Review Top Ten Reports The three most popular filters are.  For a complete list, please see Internet Filter Review Top Ten Reports:

1. Net Nanny

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Remote function: Administrator can be anywhere in the world with a computer and Internet connection and access activity logs to make configuration changes.

Uses Dynamic Contextual Analysis to filter web content. In other words, CNN.com might be blocked in the morning because of a very violent news story. However, an hour later, when the website content changes, the site will again be allowed. This software also has the option of a “warning” function as opposed to a “blocking” function. The user receives a warning of objectionable material, but then is permitted to proceed without interruption or restriction.

Will notify parents of objectionable content viewing via e-mail

Easy to use interface with clear labels.

2. CyberSitter

Will scan hard drive for objectionable content.  

Searches and finds spying programs

Also includes basic e-mail-filtering feature.

One useful function that is available that none of the other products have is the ability to scan your hard drive for objectionable material. It also will find any types of spying programs that may have been installed on your computer, either inadvertently or intentionally. CYBERsitter also had the most features out of any of the products reviewed. CYBERsitter was the only product to include a basic email–filtering feature, even though this feature wouldn’t replace a typical Spam filtering product.

3. CyberPatrol

Allows user to profile for sites and keywords.  
Did not offer reporting of Internet activity

It is not easy to get past a block (no immediate override function).  
Technical verbiage associated with proxy settings could be frustrating for average user.  

Easy to install.