Babble List the Web design and Web development mailing list
css-d list one of the best, most helpful and most newbie-friendly lists around. Eric Meyer runs it and he keeps it on track and going smoothly. It is high traffic, but even if you just save the list messages to search thru for answers, it's a great resource (and if you've got a GMail account, the Google GMail search is perfect for this list). Plus, checking out the urls posted there will get you all kinds of helpful websites plus checking the urls in people's sigs will give you great inspiration for your own sites. There is a public Wiki with tons of info and links and there's public, searchable list archives too.
Designers Talk web design forums for web designers
SitePoint Forums Resources, Design, HTML, CSS, PHP, ASP, MySQL and more for your web site
Tips harvested from theList at evolt.org
The Web Designer's Forum web design discussion list
Web Standards Group Discussion List
Content Management Mailing List
This website and list sign up is one of the most difficult to navigate that I've run across. Most sites for web design lists are professional looking and easy to get around but this one just sucks rotten eggs. There's also no NoMail option and the only way to unsub is to delete your WSG membership entirely.
WebDesign-L a mailing list community created in early 1997, a forum for those involved in creating the Web - whether for business, for self-expression, or for exploring the possibilities of a new medium
WebPro mailing list, an open, non-moderated mailing list for professional webdesigners and webdevelopers, founded in April 2004 as a companion of the FlashPro mailing list (while both of these say you should join only if you're a professional webdesigner or flash developer, there's no harm in joining and lurking - or if you do post, make sure it's in a professional manner and don't post any links that aren't to a professional site you're working on.)
Wise-Women, women-oriented but men are allowed and welcomed, activity has kind of died off tho and the website isn't being updated as often as it used to. The listowner is Dori Smith, author of the Visual Quickstart Guide to Javascript.
Women Designers Group has a list on Yahoogroups which used to be one of the best places, both for web design and friendships but sometime in 2003/2004 while I was unsubbed for a period of time, they closed up and became downright unfriendly. The original listowner, Susan, moved onto other things and you can't join now unless you have a portfolio of paying clients. Their website isn't being updated much either.