There are a lot of ways to market on the net. For a lot of sites, search engines may be the best traffic generator there is.
Search engines permeate the net.
If you don't get in to the major search engines you're automatically excluded from a number of other directories. Try AOL NetFind and you're using Excite. Search engines use all sorts of technologies including items like keywords, weighting, proximity, and full text search. Don't underestimate the human factor in searches, if you know people refer to your content area by a particular name or description, use that in a meta tag and in the description of any directory submissions you make for your site. The more you think like your readers, the more likely potential readers are to find you.