Alltop is a new (2008) endeavor by Will Mayall, Kathryn Henkens, and the famous Guy Kawasaki, the same crew that built the Trumours site.

Alltop is an organized "top sites" feed-reader, categorized and hand-picked. They have a category just for podcasts here:

http://podcasts.alltop.com/

You can't add your own feeds, but it seems they have a plan for keeping the most relevant and high-quality feeds on the page. Give it a look and see what you think.

Podcasting has grown large enough and fast enough to garner the attention of the larger marketing research firms, and the latest 2007 results are in.

2007 Arbitron/Edison Media Study on Podcast Consumers, 
Slide Show Summary
 (PDF)

Comscore's results of an iTunes podcast audience study, May 2007.

And, some results from last year as well as 2005, for comparison:

PEW Internet & American Life Project's
 Podcast Downloading Research Report, Nov 2006

Arbitron/Edison Media Study on Podcast Consumers, 2006.

Older Stats:
Google Answer from 2005 for podcasting stats - with lots of leads to track down new stats:
http://answers.google.com/answers/threadview?id=597303

Also from 2005:
http://www.pewinternet.org/pdfs/PIP_podcasting2005.pdf

Podcast entrepreueur Paul Colligan is passionate about the business side of podcasting. His blog presents daily ideas for making podcasts that make money.

He also produces My Podcast Center, a podcast directory website that also includes directories of a broad range of podcast services, including podcast creation tools, voice talent, hosting services, events, and more.

Podcasting News is a comprehensive site including a podcast directory, podcasting resources, more links, and of course, industry news.

"Promoting podcasting for everyone", including postings about educational podcasting. Ryna Irelan is the host and main writer of this good-sized website. Visit Podcast Free America