Sometimes you stumble across an excellent resource and immediately know it will be of great help in ITGS. I was really happy then to discover the IGCSE ICT site yesterday. The site offers a comprehensive topic list, with each topic clearly and thoroughly explained. Many of the pages include multiple diagrams, examples of how the technologies are used, and their potential problems. The level of detail is similar to many revision guide textbooks I have seen for other subjects. I can see this being a great help for students learning the fundamental topics (sections 3.1, 3.2, and 3.3 of the ITGS syllabus). It should also be useful for revision before the final ITGS exams.
Being IGCSE focused, the topics do not all correspond to the ITGS syllabus. However there is good coverage for the fundamental topics (hardware, software, and networks), plus several others such as IT and Health, computer models, and the Data Protection Act.