Which languages can you speak? Or which do you want to learn?
I took Spanish for seven years and was pretty much fluent, but it's been a few years since I've studied it formally so I've forgotten a lot. I'm taking Japanese now, it's my second year.
I think taking something like Russian or Korean would be fun, from what I've heard they're very flowy and pretty sounding languages. Learning Vietnamese would be nice though too, I know quite a few people that can speak it and it'd be fun I think.