HN review will give you a good sense of how useful your “fancy” application is, this is paramount to whatever promotion you may want to take your product into. Good review on HN gives you a strong launch pad, I speak from experience. You may get meaningful coverage over the internet, better than what mass mailing, spam posting and any other free platform will do.

Other alternatives are places like techcrunch ; there you must be one in the circle or getting a funding scoop. Or at best they will write in an effort to bury you instead. :-)

Target target target. Before you build your app, you should identify a dozen or so forums, mailing lists, or blogs where people talk about products like yours and would like to hear about your new website. Pretend you're your customer and Google for the problem your product solves.

Then when you release, you're just letting people know that there's a better way to do things.