I have used many of the ideas that are in the first post. They work great.
I own www.thunderbayfishing.com and have started events with my site. Such as a bass tournament. This tournament took right off. Registration is done on my site. I also have another tournament using my site as a registration place.
Other things that will work and maybe you can try them they worked for me.
I have organized a river clean up. This is also treated like a member meet and greet. The real bonus is newspapers, T.V. News and radio stations will scoop this stuff up and by getting your hands dirty you can get a ton of free advertising!
I have left posters for my site at bait shops and tackle stores. This really moved the traffic to my site.
Word of mouth is the big ticket for me. I have had some free give away contests on my site. They are only open to members and this really helps to encourage new sign ups.