Many disciplinary communities run Listservs. These are email-based discussion groups where people debate topics, exchange information, review books, publish conference reports, ask for advice, share syllabi, bibliographies, etc. Academic listservs are often used to post announcements of conferences and fellowships.
You can usually join a listserv by going to the listserv homepage, which will contain information on how to subscribe to the list by sending email to an automated Listerserv.
Often these listservs archive discussions, so you can search and view all the messages sent without having to be a member of the listserv. This can be quite a valuable way of finding information. It is often easier to view logs of the discussion on the web, than joining a listserv and having one's mailbox filled with messages one hasn't time to read.
Lists of Listservs
There are several general indexes of listservs that you can use to search for Listservs that might interest you. The main ones are:
The H-Net Discussion Network http://www2.h-net.msu.edu/lists/
This is an extensive index of mostly U.S.-based Humanities discussion groups. It describes itself in these terms: "H-Net's e-mail lists function as electronic networks, linking professors, teachers and students in an egalitarian exchange of ideas and materials. Every aspect of academic life--research, teaching, controversies new and old--is open for discussion; decorum is maintained by H-Net's dedicated editors."
Mailbase http://www.mailbase.ac.uk/
Mailbase is an index of "electronic discussion lists for the UK higher education community", with over 3000 discussion lists.
Linguistics Lists
http://linguistlist.org/lists.html
The most comprehensive index of lists related to all aspects of the study of language and communication, from sociolinguistics to computational linguistics.
JISCMAIL list of lists Index of discussion lists in the UK on range of Humanities and other topics.
Lists Relevent To Rhetoric/Comp
H-Rhetor
http://www2.h-net.msu.edu/~rhetor/
H-Rhetor is "a forum for scholars and teachers of the history of rhetoric, writing, and communication".
A listing of rhetoric and communication jobs is published every Friday. You can read and search archived logs of H-Rhetor
WPA Listserv http://lists.asu.edu/archives/wpa-l.html
"WPA-L is an international e-mail discussion list intended primarily for individuals who are involved in writing program administration at universities, colleges, or community colleges." Archives of the discussions can be searched at http://lists.asu.edu/archives/wpa-l.html.
The Pre-Text List http://www.pre-text.com/ptlist/index.html
"The Pretext Conversations" - records of discussions of composition and rhetorical theory caried out on the Pre-Text lists
Communication Research and Theory Network (crtnet)
Managed by National Communication Association. To subscribe send email request with your name included to: crtnet@natcom.org
CCCC-Talk CCCC-Talk is an open list for members of the Conference on College Composition and Communication, and for others who are interested in rhetoric and composition scholarship and teaching.
The Linguist List
Focused on 'general topics in linguistics', this list is the most widely read list in the field of linguistics.
Grad Talk Grad-Talk is a discussion list created especially for graduate students in English studies.
Purtopoi - Rhetoric, Language, Professional Writing
"A scholarly forum for the discussion of current issues, or "topoi," in the fields of rhetoric and composition, professional writing, and language research." To subscribe send the message "sub PURTOPOI your name" to purtopoi@vm.cc.purdue.edu or listserv@vm.cc.purdue.edu
Sci-Tech-Studies (STS) http://listserv.surfnet.nl/archives/sts.html
Sci-Tech-Studies is a moderated discussion group sponsored by the Science and Technology Section of the Association of College and Research Libraries.
Mersenne
This list promotes "informal and open discussion within the community of science, technology and medicine studies. We welcome interdisciplinary contributions that treat these subjects in their cultural and social contexts."