English/Technical Writing: No matter what graduate program you go to, you will have to write a lot. From grant-writing and journal articles, to research proposals and your dissertation, you will have to write a lot. Having good language skills is a must in graduate school and you might as well get practice now. I’m not sure how much of a selling point this is on an application, but the skills you gain could be valuable.
Math: As a graduate student you will have to take quantitative statistics. If, for some strange reason, you are both good at stats and enjoy working with numbers, then you could make a career out of statistical analysis.
Computer Science, Philosophy, or Anthropology: These may be less intuitive choices, but for the field of cognitive science they make perfect sense. Cognitive science is a relatively new discipline that is the study of intelligence (or mind). Researching learning, memory, language, perception and artificial intelligence. The field is actually very interdisciplinary, and research seems to come from a lot of disparate sources. Outside of cognitive science these fields might still be useful, philosophy for example could be used in the emergent field of neuroethics, but I wouldn’t count on them being a big draw for the majority of graduate programs.