I know this is a bit off topic, so vote me down if need be...
But have you ever considered advertising on public transit? It's actually cheaper than you might think. I'm from Toronto and recently came across this article about advertising on our subway and tram system called the TTC: http://www.blogto.com/city/2010/10/ever_wondered_what_it_cos...
It might be worthwhile to check out your local subway system, if that form of advertising would hit your target market.