Neuroscience is a field both new and broad. It has roots in psychology, cognition, molecular biology, psychophysics, and more. Although there are some (slightly self-serving) attempts at defining what the open questions are, the sheer diversity of the field lends itself to many possible questions. The answer for those interested in psychology, in economic behavior, in ecology, in vision, in molecular biology, will all be different.
Regardless of field: what are the most important open questions in your field?
Feel free to respond in the comments, on twitter, or on your blog.