What is the best way to advertise a web application or site on the web, specifically paid advertisement, but if there are any great free ones, those are welcome as well. Please refrain from mentioning meta tag's and technical SEO related site modifications.
Google ad-words is one way we all know about. But I'm looking for other suggestions that have worked well for you or someone you know.
Since this is subjective, I have marked it a community wiki.