[email protected]
http://listserv.acsu.buffalo.edu/archives/autocat.html
This is a fairly active list -- 20 or messages a day, so if you miss a few days, the messages pile up. If you're really interested in cataloging, this listserv is a must. It covers a wide range of cataloging and classification issues, both theory and practical aspects. Sometimes vigorous discussions on things only catalogers could care about, such as use of the serial comma, or the proper spelling of the word catalog (vs. catalogue).

025.431: The Dewey Blog
http://ddc.typepad.com/025431/
Written by members of the Dewey editorial team at the Library of Congress. They often take a topic in the news and explain where it would be classed in Dewey and why. There are usually three or four posts a week. The Dewey team is not without a sense of humor.