E-mail - E-mail can be a powerful tool in bringing members back to your web site and give them other valuable information. A lot of web sites have a monthly newsletter where they can keep their users informed of what is going on with their web site as well as promote other services and other web sites they might be interested in.
I have used all of the above traffic methods, but have had more success with some then others. I started out using Paid Search Results to get my first web site additional traffic. I later moved to Referrals as this was much more cost effective for me, I found it to be less expensive since I only had to pay when a user signed up and not just for clicking on the link. I also liked the idea of keeping everything “in house” and not having to pay another company for their services.