I did Philosophy, it's fun, probably good as a 5th subject. Most people that take History like History, as well, so maybe that...
Spanish is well good, but hard.
Maths is okay, I did stats. Don't take it if you're not really a fan, though.
Chemistry is good if you like that kind of thing...
Eng. Lit. is really good, even though I hated it at times, it's fun and fairly easy if you like reading and can learn a few buzzwords.
I'd say History/Eng. Lit, Spanish, Psychology (seems popular enough), maybe Biology or Chemistry or Maths (only if you like Maths, though), and Philosophy if you're taking a 5th.