Newsgroups offer the same PR opportunities as discussion boards and generally the same etiquette applies. Professional associations often have web sites with a plethora of information. Quite often they will publish profiles of officers, committee members and event coordinators. Get to know these people by commending them on their efforts. Contribute opinion and volunteer where possible.
Associations typically have community events, guest speakers, newsletters, etc.
Finding out about them and getting involved has never been easier. Take a look at what your competition is doing to get ahead. You'll be surprised at how many are doing little more than buying ad space. Ads have a much lower click-through ratio than text links that you can get from contributing your opinion and don't do much for building credibility. People are more likely to click on a link to your firm's site if it's associated with a newsworthy piece of information.