Well then, the other question to ask is this: What aliens outside of the Star Trek universe would the Borg take an interest in?
As I mentioned in the first post, the Time Lords from Doctor Who would undoubtedly have plenty to offer the collective. Their technology is highly advanced and their biology is unique. Their knowledge of other cultures and interstellar phenomena could even rival that of the collective itself, and of course they are masters of time travel. I imagine that the Time Lords wouldn't go down without a fight, of course. Plus with their ability to regenerate (which as yet has no proper scientific explanation for), they might not even be susceptible to standard assimilation methods.