What is Podcasting?
Defined in Wikipedia
One of the better overviews of podcasting and its origin (Podcastalley)

Podcasting in Education
Educational podcasting directory (Podcastingnews.com)
Podcasts for educators, schools and colleges (U.K. directory)
Resources for educational podcasting (Bernie Dodge, the webquest guy)
Podcasting Library at the e-Learning Centre (excellent U.K. resource)
Podcasting in Education (Apple)

How to Podcast
Podcasting for the technically astute (Engadget)
Podcasting 101 (Tod Maffin's "I love radio")
Audacity Recording Tutorial (Flash based tutorial developed for a Blackboard project)

Podcasting software, tools, etc.
Podcasting Tools - Comprehensive resource for podcasting

Podcast aggregators/receivers
iTunes - Arguably the most ubiquitous cross-platform podcast receiver +
iPodder - FREE Popular cross-platform podcast receiver (Mac/Windows/Linux)
iPodderX - Great podcast receiver try/buy (Mac OS X)
Pluck - Award winning FREE news aggregator. Runs in IE (Windows & Web based)

Blogging hosts
Wordpress - Open source personal publishing platform (Podagogy platform)
Moveable Type - Popular, but no longer free
Blogger.com
Informative Article reviewing blog platforms and blog hosts (About.com)

Podcasts from the inventors of podcasting
Adam Curry's Daily Source Code - from the "Podfather", co-inventor of podcasting
Dave Winer's Morning Coffee Notes - from the other co-inventor of podcasting

Podcast Directories (Available Podcasts)
Podcast.net
PocastAlley
Latest 100 Podcasts