The Astronomy Picture of the Day, or (APOD), is a website hosted by NASA which uploads daily images of the wonders of the universe, from pictures of the planets in our solar system, to stars and nebulas, to other galaxies. Each day's' image also comes complete with an explanation by a professional astronomer, highlighting interesting and little known facts. Links to previous related posts further help visitors learn as much as possible about astronomy during their visit.
APOD's site is apod.nasa.gov
The Hammock Physicist is a witty and yet thoroughly insightful blog about all things physics. Written by Johannes Koelman, a theoretical physicist, each issue discusses some recent discovery or longstanding mystery, offering the unique viewpoints from a scientist's spare time.
Koelman's blog, which can be read here, is hosted by Science 2.0, another great website for scientific news as well as blogs and columns from specialists in all sorts of fields.
ArXiv.org is a massive open access online source for scientific research articles of all disciplines, including physics. Although not all articles are peer reviewed, contributors take their work very seriously, and must also be backed by an endorser to ensure quality and pertinent work. Many articles go on to be published in peer-reviewed journals, while others remain free to be viewed by any interested reader.
ArXiv's site can be found at www.arxiv.org
There are a ton of online magazines dedicated to the propagation of scientific knowledge, each one sharing the latest discoveries in clearly explained, entertaining, and sometimes interactive formats. From news about planets orbiting pulsars to in-depth seismology to the wonders of biology, these sites make the intricacies of our world, and the universe at large, available to everyone.
Many professors, researchers, students, and enthusiasts have turned to the internet as a means of sharing their passion for science and insuring the spread of factual - and really cool - information about physics. The following links are a few great examples of such podcasts at their best.
XKCD is a wonderfully clever webcomic by former NASA Roboticist Randall Munroe. The comedy mostly revolves around science and math, both entertaining and educating readers in the span of a panel or two. If you haven't heard of it yet, enjoy. I promise, you will be hooked.
