try www.pilots4rent.com - they are really looking for high time, experienced contract pilots, but I've seen a few CFI ads over there. They may want you to join the IACP (International Association of Contract Pilots) and I did, but they STILL haven't cashed my check 6 months later. I would rather they did, as I hear their newsletter is excellent.
NAFI also has a site for advertising. I am listed on jetcareers, AOPA, NAFI, and Gleim, but have had nobody say they found me on those sites. I am about to build my own web site and see if that generates anything in the future. I am keeping busy right now, though, so I guess I can't complain.
I'm listed with Gleim and AOPA and I think another one or two. I've never received a referral from them. On the other hand, most of my students, as well as the ones that I've referred to other CFIs have come through my web site, either through a general search or through my participation in forums like this one.