Here is a great set of revision videos by Geoff Riley of Tutor2u. They cover a range of macro and micro topics for AS and A2 Level economics. Most of them are around 8 minutes long and he uses the powerpoint slides very effectively so you get his oral contribution plus the key points on the presentation slides. Well worth a look and you are bound to find them very useful as exams approach. Below is the video on the Circular Flow.