Have you thought about pay per click programs? The two biggest, I think, are Yahoo! and Google
A few free resources – check out the sources box for links:
1) Create a blog pertaining to your field
2) Use Yahoo! Local & Yahoo! Groups – Be sure to read the TOS for each one!
3) Write articles pertaining to your field and/or expertise.
Also, consider signing up for an affiliate program. These programs enable you to advertise on other's sites (your affiliates) and once a sale is made to you, your affiliates & the program are paid a commission.
I listed a few handy sites & articles relating to marketing, promotion & advertising. Here's some book titles that are relevant:
* 301 Do-It-Yourself Marketing Ideas: From America's Most Innovative Small Companies by Sam Decker
* Off The Wall Marketing Ideas: Jumpstart Your Sales without Busting Your Budget by Nancy Michaels, Debbi J. Karpowicz
* Guerrilla Marketing for Free: Dozens of No-Cost Tactics to Promote Your Business and Energize Your Profits by Jay Conrad Levinson
* Entrepreneur Magazine's Ultimate Small Business Marketing Guide: Over 1500 Great Marketing Tricks That Will Drive Your Business Through the Roof by James Stephenson
Hope that helps! I wish you much success & happiness in all your ventures!