I think rectangular glasses for a businessman are appropriate. The glasses with conservative frames and colors are the best for businessmen, for people of this career should give a trustworthy and staid impression to others. Oval, rectangles and almonds frame shapes are preferable for glasses for business. The frame colors shouldn't be bright or flashy, and you'd better choose low-profile colors such as gold, silver, brown, grey and black. I suggest you to wear glasses with frames of these colors also because they are easily matched with your business suits. I recommend Danish Eyewear style M791 to you, for it will give you an elegant and confident look.