You can find past papers and lists of useful resouces on the Cambridge International Examinations website. On this site you will find Learner guides, containing revision tips and examination tips. There are also links to interactive simulations and games, and science resources which you can download for free.
New IGCSE, AS/AL and OL Learner Guides have recently been added to the site. To find them, simply select your subject from the left hand menu bar and select IGCSE, AS/AL or OL.