Fredrick Griffin led to the discovery of DNA by showing us that bacteria can change their function and form through transformation. He found this out by studying two different strains of bacterium: R(rough) strain and S(smooth) strain.
Oswald Avery contributed to the discovery of DNA by declaring that DNA can change the property of cells. He also figured out that genes and chromosomes are made from DNA.
He established two rules, later known as Chargaff rules. His rules said that in natural DNA the number of guanidine unites equals the number of cytosine units. The second rule is the the number of adenine units equals the number of thymine units.
Maurice Wilkins also used an X-ray to produce diffraction images of DNA like Rosalind Franklin. The only difference between them is that Wilkins was able to share the 1962 Nobel Prize in Physiology or Medicine with Watson and Crick.
Rosalind Franklin's work with DNA diffraction helped her figure out that DNA has a double helix. This later helped Watson and Crick steal her work pretty much.
Martha Chase and Alfred Hershey
They discovered that it is DNA and not proteins that is the genetic makeup. They helped the world figure out that after a particle attaches itself to a bacterium, the DNA enters through a hole while the protein coat remains outside.
James Watson & Francis Crick
They were famous for "discovering" the double helix structure of DNA. They ended up winning the Nobel Prize in Medicine in 1962 for their "work".