I wish I could find a good source for Taiwanese, would make conversations with my in-laws much easier. Spanish may be interesting, but not sure how much I would use it, don't really get out much. I am planning a trip to Europe where we'll be going to Germany and France, might decide to brush up on my German, my wife majored in French, though can't speak too much of it currently.
Already fluent in Mandarin :-P If anyone wants some tips for that I'd be glad to give a few pointers, especially with reading/writing.