British Naturism
To get access to the website you have to become a BN member which costs around 30 per year for a single membership (I say around because there is a reduction for direct debit payment).
For that you get 4 good value magazines and the chance to meet other folks at the various gatherings that take place. Plus advice and help if you go free-range and get into legal problems.
The forum is quite lively (in amount of posts and posters, and more or less troll-free), it has a good amount of advice on there and in my opinion is well worth the money.
JimDoug, one thing I forgot to mention is that if you are trying to sign up at any of the naturist clubs the card gives you a little extra credibility. Also it gives you INF membership for what that is worth, which from what I have been told makes it easier to book on foreign trips.