I have just finished the development of my application. Now I would like to promote\publicize that (I have no money!). What are techniques most commonly used to do that on the web? And the most efficient?
Create a website with appropriate landing pages, designed to market your application. Then the internet really is your oyster.
Collate emails however you can, if you'd have had a large email list of recipients who might have found your application useful that would have been a nice kick start. Concentrate on SEO for the site featuring your web app. Create discussions about it in relevant forums... The list really is endless.
Facebook is one of the greatest bridge that can get you app discovered. It's also the best way to practice the "pass the word" approach that you're talking about because you know who you will be talking to, your friends which will also recommend the app and then the dominos will continue to tip down... :))