There is also the British Titanic Society; many of its members are on this Board.
I plan to attend their 2007 Convention. There have been a lot of positive comments about the festivities. The only thing is to be careful not to doze off in the Hotel lobby, especially if you happen to be a Titanic historian; there's a few comments about that story in the other threads.
There's a list of many Titanic societies around the world here. Although created in 2001, it has been updated somewhat recently---at least within the last year, year-and-a-half, or so---since it reflects the change of the Belfast Society's name, which took place in 2004, if I recall correctly.
Thanks For Your Opinions. I've decided I'd like to go w/ THS, and im Also giving TIS Serious conideration, mainly because it's in the U.S. I will howver be glad to give other societies consideration (Cost, Background, Benefits in being a member, and any other sort of info that might be useful). anyone who thinks they have info which might be useful to me feel free post here, refer me to a post, or contact me privately.