Harry Gensler's Ethics - an excellent site to accompany his book: Ethics: A Contemporary Introduction; includes lots of interactive questions to allow you to test yourself. You can download the tests and the programme even keeps your score!
Tutor2U - a real find! This site has excellent content for the Philosophy and Ethics A level. The site looks dull, but the notes are easy to find and print out. Don't waste time looking for RS quizzes etc. - all the tests are for Economics, Politics, Business etc.
Wikipedia - THE free online encyclopedia. You can find out anything about anything here, and it is reliable (although because it's American, the terminology is sometimes unexpected). There are over a million articles!
rsrevision.co.uk - this site has some good content, but is spoiled by infuriating adverts. To save time (and frustration), download the site's Philosophy and Ethics notes