When these periodic "let's put a woman on a bill" come up Noether is my choice for the subject. Her work had a huge influence on the shape of the world today and few people outside physics and mathematics have heard of her.
United States currency has the inscription “In God We Trust” in a place the Secretary decides is appropriate. Only the portrait of a deceased individual may appear on United States currency and securities. The name of the individual shall be inscribed below the portrait.
See the FAQ [2] at the Bureau of Engraving and Printing site for some interesting information on how the current choices came about.
[1] 31 USC §5114(b)