I know this poll is old but I had to answer. I love Japanese and Klingon, but I really think American sign Language is cool. It just looks really cool for some reason. Plus efficient in some cases such as underwater communication.
Well, I know a few websites on it but I haven't had a lot of time to really learn it since I'm learning several languages at the moment. Though I know basics. Like hija, ghobe, and the phrase "TaH pagh, taHbe" 'To be or not to be."