Beethoven’s Symphony No. 3 “Eroica” – A wonderful website devoted to one of the most important pieces in Beethoven’s career, and the history of the symphony. Courtesy of Michael Tilson Thomas and the San Francisco Symphony Orchestra, the website also features works by Copland, Tchaikovsky and Stravinsky.

Flash Earth – View the Earth using Google Earth, Microsoft Virtual Earth, Yahoo! Maps and more, and switch between them. The site claims to be experimental and works without official consent, so will not necessarily be around for long.

Tenth Dimension – Confused by string theory? Watch this simple and fascinating video explaining the ten dimensions—but be prepared to have forgotten it all inside of two minutes!

Zamzar – Convert between a good variety of audio, video, image, document and storage file types online for free. This includes videos available on a number of popular websites (e.g. YouTube, Metacafe and the like). The paid for version offers a number of improved features, but even the basic free version allows files of up to 100Mb to be converted, plenty adequate for most file types, though the result is emailed to an address of your choice, which could prove problematic for certain inboxes.