Now alot of teachers and professors will tell you that wikipedia is NOT a good source for information, and they are right somewhat. But in my opinion Wikipedia is a very valuable online resources to learning information. Just make sure you use it wisely and it is NOT a credible source for research papers.
Also, you may be compelled to Google questions in your homework. And this may find you the right answers quickly, but it is not helpful for learning the material at all and I don't recommend it.
Heres a list of helpful online resources:
www.wikipedia.org
www.sparknotes.com
http://www.wolframalpha.com/
http://www.merlot.org/merlot/index.htm
