The following websites are for general revision purposes. Every subject teacher will be able to supply you with more subject specific website links.
CCEA Microsites - http://www.rewardinglearning.org.uk/microsites/
BBC Bitesize - http://www.bbc.co.uk/schools/gcsebitesize/
Study Support, Brightsize http://www.brightknowledge.org/knowledge-bank/study-support
GCSE.com - http://www.gcse.com/
Revision world - http://www.revisionworld.com/
The Student Room - http://www.thestudentroom.co.uk/
Belfast Telegraph, Surviving exams - http://www.belfasttelegraph.co.uk/news/education/surviving-exams/
