History Learning Site - This link takes you to the GCSE modern world history pages of this site. A little boring in its layout, but it covers all the necessary information and can be used as a helpful supplement to the textbook.
Spartacus History - This is a huge site with plenty of internal and external links. This link takes you to the home page. Use the topic headings on the left to go straight to such items as Nazi Germany, or the USA between the wars. There is a long lists of external links at the bottom of the page - click on the third one, "General Websites 14-18+" for a relevant selection of links.
BBC Bitesize - This is a user friendly site and well organised, if a little bit light on detail. Good for 'overview' revision, but not enough on its own for 'depth' revision.
BBC History pages - The BBC has an excellent range of general history pages. Use the search box at the top to find links to specific topics. More for background reading and knowledge than straightforward revision though.
School History - This takes you to the GCSE links, giving a good range of different topic links and some resources to use for revision (downloadable lessons, presentations etc.) which are on the right hand side!
The Cold War - Excellent CNN website, linked to their 'Cold War' video series. Of particular use is the Episode guide, which takes you straight to a useful collection of material supporting each episode, as well as both an overview and the full transcript of the episodes, which can add immeasurably to your store of knowledge.