I worked for a company who used to do side jobs all of the time except we called them beer money jobs. We did a few things to promote ourselves:
1) Check out Service Magic online. It's a good way to get several leads. They send you an e-mail, and a computer generated call will go to the phone of your choosing (home, cell, etc.). Cons - You get charged $20-$25 for each lead that you receive. It's great at first until you realize that 3-4 other engineers get the same leads. You still get charged for receiving the lead even though you may not do the actual work. The best way to get the most work is to call up the client right away.
2) Realtor Rallies. I don't know if IL has any of these, but Denver hosts a rally each year. Several hundred realtors will show up and check out your booth/previous work that you bring. Very few engineers actually have a booth, but a lot of home inspectors do. Take a break once in a while to walk around and talk to the home inspectors. These guys are likely to send you more work than the realtors. If you work with realtors, they generally will want a report with any repair details and calculations within 48 hours of your visit.
3) I agree with Santiagj about Craigslist. It's free advertisement, so you can't go wrong there.