Since most things concerning coding etc. in IM are very easy (as in you don't need to take some advanced algorithm class to do it), I would only go with CS if you are really interested in the theory behind computers (and/or are looking to do some startup heavily relying on current research stuff in CS).
I'm biased (since I did it), but I really think that studying finance helps you understand a lot of stuff about markets, companies, biz models, applied maths, stats, etc.
Another possibility would be psychology.
All in all, my advice would be to choose something you like since no-one will stop you from learning what you need on your own, but its hard to learn something you aren't interested in.