I have collected below a list of 13+ Common Entrance revision websites, apps and podcasts. However, this is not an exhaustive list so please contact me if you would like any additional pointers. I can offer more detailed advice on specific subjects, and I have compiled my own revision notes for some of them.
13+ Common Entrance Revision Websites
Religious Studies: Common Entrance Religious Studies Revision.
In addition, the BBC website has a wealth of appropriately presented and useful information (and games) on a variety of topics; relevant links can be found here (Key Stage 3) and here (GCSE). Of course, these resources are geared around the National Curriculum and not Common Entrance, so you will have to pick and choose a little. Those preparing for a scholarship would be wise to pay a daily visit to the BBC News page; younger pupils may enjoy the Newsround page instead.
13+ Common Entrance Revision Apps and Podcasts
English, Maths, Science, History, Geography, Religious Studies: Gojimo revision app by EducationApps. Individual subjects can be added freely within the app. However, this works only on newer devices. Older ones can use 13+ Common Entrance Revision also by EducationApps; this uses the same quizzes but they are available as in app purchases.
Religious Studies: Revision Podcasts from www.ce-rs.com.
A few other relevant sites include...
The Independent Schools Examinations Board is responsible for setting Common Entrance and Common Academic Scholarship papers.
Galore Park publishes Common Entrance text books. They are also the official purveyors of Common Entrance past papers.
The Good Schools Guide contains a range of help and advice on almost every aspect of education.