In the early days of the Internet, one of the best ways to market your business online was to appear often in Usenet Newsgroups.  These are bulletin board like discussions.  They can still be a good and often overlooked marketing opportunity.  Blatant advertising is usually banned, but you're welcome to give advice, pass on information, and include your four to six line "sig" file of contact info at the end of each message.

Newsgroups are a good way to build a reputation with a limited, but influential, group of people in your field.  Pick no more than two groups to participate in.  Try to post messages at least twice per week.

Don't let the "Troll under the bridge" discourage you.  Just about every Newsgroup has one or more Trolls.  These are people who seem to live on the Newsgroup and make a career out of attacking anything you say.

A good string of Troll attacks can actually draw attention to you and send legitimate customers your way.

Look for an abandoned group you can adopt and promote.