Khan Academy is absolutely fantastic!
My younger sister recently turned me onto this website called http://www.khanacademy.org. This site has numerous videos – over 2400 as the introduction states- that cover a good range of topics from math to history. These videos are available to anyone and everyone who is interested in learning something new or someone who just wants a refresher. The videos are mostly 10-15 minutes long, some are a bit longer and few shorter.
The man who started and developed this non-profit organization, Salman Khan, is absolutely wonderful at explaining and simplifying a seemingly difficult subject like trigonometry, Chemistry, finance and my new favorite Biology.
Check it out, its worth the second it takes to click on the link🙂