Currently, there are two options for the Custom Search. The default option is free, hosts mandatory ads and is branded by Google. It has the ability to search the web. The second option is paid, has more advanced options and makes branding/ads an option.Search engines created with Custom Search can be monetized, by using the PPC ad method. There is, however, the fact that businesses may suffer from this, as ads may go to competitors pages.
Subscribed Links are web results that users can manually subscribe to. Anyone is allowed to make a new Subscribed Link, and do not necessarily need knowledge on how to create a feed, as a basic link can be created. Subscriptions are then available in a special directory.  This service has been discontinued.
Topics are specific areas of search, which can be developed by people with knowledge of a certain subject. These topics are then displayed at the top of relevant Google web searches, so the user can refine the searches to what they want. Currently, there is a limited number of topics that Google is wanting to develop, namely Health, Destination Guides, Autos, Computer games, Photography and Home Theater.
One of the topics with many contributions is Health. They include the National Library of Medicine, Centers for Disease Control and Prevention, Health On the Net Foundation, Harvard Medical School, Mayo Clinic and others.
A typical example of custom search engine is AllGameSearch . This is the google powered custom game search engine exclusively for game industry.