Ask HN: Best places to advertise online

I think the best places to start are places frequented by your target audience. That may be a place as big as Facebook or as small as a antique automotive forum.

If you don't know what audience you're targeting, that is probably a bad business strategy...but if you want to do a little research, put some ads on a 'broad-spectrum' website like Google, Facebook, Twitter, etc. and then run some stats on your web server logs after a while. They'll be able to tell you where your traffic is coming from, what people are searching for to find your site, and so forth, which you can then use to better target your ads, etc.

I will recommend http://en.wikipedia.org/wiki/Cost_per_action