My recommendation is to get the app reviewed by several of the well known bloggers like:
http://appadvice.com/reviews
http://www.148apps.com/
http://gizmodo.com
Etc.

Your short term goal would be to get 20 to 25 reviews on blogs and online media sources.

As well run 2 to 3 major press releases in regards to your application and how folks use it.

Great low cost marketing should always be done with high quality advertising and done together you will gain the kind of traction you are looking for.