This site is not the most sophisticated on the web, nor the largest - in fact there are not many people in it. But it has better security than any other I've seen. Tells you where the last log in was from for each person, likelihood of a scam (based on a number of factors - eg message has been cut and pasted and sent x times). It also has some very useful hints about how to check - like how to check where an email originated - very useful.
They also have a new IM system which looks like it will be really good but does not seem to work right at present (for me - maybe I got it wrong).
Lack of members