In a house that age, just about everything - roof, plumbing, electrical, foundation, general structure, heating/air conditioning, installed applicances that convey, etc.. You may want to consider getting several different inspectors that specialize in specific areas. Earlier this week I had a buyer show up with 5 inspectors for the initial inspection (swimming pool, roof, electrical, plumbing, general). You may also want radon readings taken, since many homes built in that period weren't vented for that. If you or your inspector detect any hints of mold, you may want a mold inspector to provide a report, also.
Best of luck!