_Paul Andersen teachers science at Bozeman High School in Bozeman, MT. He is the 2011 Montana Teacher of the Year. This link is to his very user friendly youtube presentations.
Salman Khan has put an amazingly powerful, yet simple, concept into practice in the website Khan Academy. Visit this to get quality, accurate video lessons on many topics in biology, but also in math, other sciences...
As with the other sites listed above, Hippo Campus is more directed at AP Bio curriculum, but although some details maybe "extra" and some details may need to be added in, the quality of the presentations is excellent.
Crash Course and SciShow
youtube 12 minute videos with entertaining presentations reviewing some basic biology concepts (and similar presentations on world history!) - CrashCourse and SciShow
This site is designed for use by teachers and students alike...great browsing and exploring! ed.ted.com
High quality animations of cell biology topics and a fabulous timeline for evolution, also viewable as a video with supporting links.
HHMI Lectures, Video, Animations
HHMI is the Howard Hughes Medical Institute, a major funding group for cutting edge research projects, but also a supporter of biology education through their website and distribution of the Holiday Lectures on topics from infectious disease to biological clocks to cancer and more.