Students often use Audacity to create podcasts.

Podcasts can be subscribed to in an RSS Reader or downloaded to an MP3 player.

Some sources for podcasts:

CBC Podcasts
Learn Out Loud directory
MacTier Public School

The Clever Sheep's Podcasting Tools wiki

Vodcasting in Education

Lots of lectures and lessons are now available on the web (e.g., MIT, iTunesU)

Presentation Tools

Google Presentations (see Scribd iPaper intro)
Many more on Web 2.0 in Education site

Other cool tools

Gcast - podcast
Voicethread - annotate and share your images, videos and presentations

Back to Web 2.0 Tools