MIT is providing a fantastic service with OpenCourseWare--they're essentially open-sourcing many of MIT's courses. They hope that the availability of lecture notes, assignments, and sample exams will make life easier for professors and result in a higher quality of teaching at universities across the world. It's also a useful resource if you happen to be a student and are wondering what kinds of material will be covered in various undergraduate courses or are looking for a leg up on your studies.
There are a full set of video lectures available for Physics 801, 802, and 803, all taught by the esteemed Walter Lewin. I guarantee watching the videos will boost your grade and understanding if you're taking a similar course at another university. They're also entertaining as hell because Lewin has a fantastic sense of humor and does plenty of live-action demos. Video lectures aren't the primary mission of OCW, probably due to the high cost of bandwidth, but it sure is a neat service to provide to the public for free.
Although the main purpose of this site seems to be to sell the software of the same name, there are a wealth of interesting opinions here. The FAQ on sleep and its relation to learning really changed the way that I think about sleep and maintaining a sleep schedule. The key idea that sleep is essential for long-term memory formation seems to agree strongly with my experience. On the other hand, I don't really think that sleeping until awakenening naturally is practical or efficient. For example, I can coast in dreamy REM sleep until I hit 10 or 11 hours a night pretty easily. I can get much more work done if I cut it down to 6 or 7 hours with an alarm, but at expense to my quality of life and probably my long-term memory, too.
Despite the fact that most of the content there isn't peer reviewed, I find it to be a valuable resource and often find myself returning when I want to remind myself of the best ways to learn and store facts in my memory.
Fear not, more sites are sitting in my bookmarks waiting patiently for a review. Until then, you can find something else to do on the front page.