I’ve been following Qwiki in its beta form, and now it’s available to all. Qwiki is a multimedia resource with more than two million entries (so far). The entries are narrated (the text appears also) with illustrations and links to other related entries. After the brief introduction to a topic, additional topics and options are available.
To use Qwiki, type a topic in the search box or select a topic from the featured topics. Here are a few science-related Qwikis:

• Volcano
• Periodic Table
• Sharks

The voice in the narrative appears to be computer-generated with some issues in pronunciation (e.g., desert animals  as “dessert” animals). I’m sure there will be improvements to this alpha version, and there is a place for registered users to submit suggestions. I can see a lot of potential for the classroom, both as an informational tool and as a creative one.