What i've seen work, craigslist ads, many of the doulas in the area teach little seminars at Babiesrus, its a great way to introduce a more "mainstream" crowd to the concept, leave cards at birth centers, anywhere offering prenatal fitness, my yoga class is always discussion doulas.
BTW, I'm not sure if its int eh terms of use to list your website in your signature, I had to remove mine since I wasn't a paying advertiser. You might wanna check

One other place you could try is the local hosptials, if they offer water birth, some require a class, maybe you could meet the teacher and network that way. Just a thought. We have LOTS of doulas in my area and its hard to get your name out there! Websites really are a great tool as well!