Have you tried promoting on Adwords, go for long tail keywords, optimize, optimize, optimize? Have you done A/B testing on your landing pages? Have you thought about installing an affiliate program?
We have done many tests with Adwords - our margins are tiny, and adwords doesn't seem to work for us. We are still testing this, but we are not even close - we are many, many miles away. I'm sure we are missing something with adwords, but we have tried a lot, but still not succeeded.
We have a very basic discount/promo system, but building an affiliate system takes time, and we haven't had any requests for it, so it is not at the top of our roadmap.
