Newsgroups and email lists are both online discussion groups. You can access newsgroups through your web browser or with a news reader. You access email lists through your email box. Newsgroups generally do not require registration so the participation comes from a wider audience. Email lists are based on subscription and therefore often have more of a community feel.
Here are some of my favorite newsgroups & mailing lists:
Nonprofit Tech Talk is for techies in the nonprofit sector. Some members are really experts; some are just learning but folks are respectful and helpful with questions from both ends.
Hidden Tech is a list of tech-related business owners in Western Massachusetts. People ask good questions, get good answers, and I’ve seen some interesting business deals getting started here.
E-Democracy hosts a number of mailing lists for local political and policy discussion. There are lists in the Twin Cities, Chicago, Iowa, and now in the UK. (If you’re not in one of those areas – you can always check with this volunteer-based group about starting a group in your area.)
Minnesota Fishing Forums gathers fishers from across the state to talk about fishing. The hot topic these days is ice fishing. I love it because so many people include pictures!
You can find a Yahoo Sponsored newsgroup here; Tile.Net is still the best list of email lists I know. Sometimes getting involved in a public discussion can be a great way to promote your web site – if done very carefully. (In other words just be helpful and include your URL in your email; don’t try to post ads, they are rarely well-received.)