Jennifer,
Spanish would seem most useful for you, but it may also help to learn a bit of others, like Mandarin. Other languages seem interesting, and i hope the resources suggested would help you. Unless you have that much time and focus on one language, you can also learn a little of French, other, for then you wont feel so uncomfortable when ppl from other nations or cultures are speaking their tongue and you have some idea of what they may be talking about and not wonder if they are selling you or what=).
A well-known French phrase is qu'est-ce que c'est, used when you want to ask what's going on. Even if you dont master the language, it is fun to know some esp how they sound. Good if you understand even if you do not really speak it.