I posted this answer in a similar questionsimilar question
I don't know how effective this idea is (I haven't tried it yet) but for my current project I am going to advertise on Facebook. Let me explain.
Essentially I am going to create a fan page, and run an ad campaign on Facebook. What I figure is I can spend like $30/mo (or what ever you want) for advertising. As people become a "fan" of the page, a lot of other people will see that. So basically, if that $30/mo generates 5 fans directly, it could generate 50 fans indirectly. I figure I could also do some fun stuff with the fan page such as give away copies, solicit ideas, etc...
Like I said above, I haven't tried this so I don't know if it will work. However, I will let you know in the near future. :)