What are the best ways to get traffic to your site?

In promoting your website(s), what are some unique free traffic methods
that you use on a regular basis?

I don't think there are any truly 'unique' methods.

Here's what we do:
Build a good product (it's constantly being improved)
Make sure that bloggers & influencers know about the product
Get other people to link to your site as an example, our widgets:
http://www.funadvice.com/syndicate/widgets
Or the plain old ask people to link to you:
http://www.funadvice.com/doc/link_to_us

Then there are the RSS feeds which enable people to 'take you with them' if they use an RSS feed reader or similar.

All that adds up to some degree of popularity, which results in search engines indexing & potentially ranking your content. About half of the people that register here are from search engines, the other half are from word of mouth.

The best, very, very best way to get consistant, free traffic to your site is to get enough people talking about it. I've probably told as many people about FunAdvice (and I own it) as any one of a dozen websites that were amazing when I found them, that I still use for the purpose which they were built for.