What engineering classes should I take in college?

[DonRotolo]

Aside from what squirrel said - all of which are excellent suggestions - you might find a course in Biomedical Engineering. There may be prerequisites which might be a major roadblock (to a Bio major), but you can audit it to see if it's over your head. There's nothing more awesome (and valuable in today's world) as an MD with an engineering degree - come as close to that as you can.

Having a background in Physics (as in Physics 101) would be valuable. You have the chemistry already (or will soon enough).

Go visit the dean of the engineering college. s/he will probably agree to a 30 minute meeting with you, and there you can explain what you're trying to do. Surely they know their curriculum, and maybe they can hook you up. (Prerequisites can be overridden, for example).