Whichever exam you need to take, I recommend going to their own websites and finding the resources that they recommend:
Cambridge ESOL (now Cambridge Language Assessment): http://www.cambridgeenglish.org/
IELTS (International English Language Testing System, adapted from Cambridge ESOL): http://www.ielts.org/
All of them offer free practice tests and sample study resources for individuals to use. You cannot use them for online teaching or redistribute them to anyone. They sometimes also offer teaching resources.
The British Council also offers resources: http://www.britishcouncil.org/
I hope this helps