Paid for advertising, $120 for a 125x125 image on AndroidGuys.com for 30 days: 200 clicks after running for 27 days
Paid for advertising on AppBrain.com, they use a pay per install system. Free version got 57k exposures and 700 installs in 12 hours, spending $25. But paying users to install your app is not good business model :-/
Puting the paid version on AppBrain.com: After about 30 days, AppBrain seems to have stopped advertising it after 20k exposures with no sales they can attribute to the advertising. It rarely gets exposure time on AppBrain now :(
Biggest marketing successes: Lifehacker article, and recently a Reddit submission.
In summary, no silver bullet that I've been able to find/control, just 'word-of-mouth'