How do you spread word/advertise a site, without paid advertisements and not be considered a spammer?

My dilemma is that I want to advertise/promote a really cool site (in my opinion, hopefully others) but would like to do so without paid advertisements initially. It’s not that I don’t have the money, I just want to see if the idea is good enough and has enough merit to take off on its own.

To accomplish this, i’ve gone around the internet had have had very very mixed responses….So, what is an effective, tactful, and most importantly, a non spamming method to advertise/promote a site?