Sometimes 'interactive' means 'get students to do a traditional multiple choice quiz on the computer', and sometimes it means 'invite students to explore a professionally produced multimedia resource which has quality content and more than one possible learning application.' Guess which sort I prefer!
The following three resources stand out to me for their depth of content and production quality. Although none was produced specifically for an English teaching context, they can all be integrated smoothly into lessons on a variety of typical topic areas - and I have used them all successfully with my classes.
Track an Email with Google Green
The first site is The Story of Send, produced by Google Green. This is an interactive journey following the path of an email from your computer, through Google's data centres, all the way to the eventual recipient. On the way, guided by appealing animated characters, you can use text, video and photo galleries to learn about data security and green technology. The text is in bitesize chunks, and introduces complex technology in an approachable way. You can also use more or less of the site depending on student level and time constraints, by skipping some of the multimedia content.