I remember learning in school that Watson and Crick were attributed with discovering DNA, but also that there was a woman who helped a lot with the experiments who is rarely mentioned.
Who is this woman, and what did she do?
The woman you're thinking of is, notably, Rosalind Franklin. Her specialty was X-ray crystallography, and she worked with Maurice Wilkins and Raymond Gosling in the early 1950s, continuing their previous work, to apply X-ray diffraction to produce images of DNA. Watson and Crick's models were built and confirmed by data gathered by Franklin, Wilkins and Gosling; the images allowed them to discount previous models and identify the double helix.
To say that Rosalind Franklin helped with the experiments is erroneous; she performed the experiments, along with her colleagues (and yes, other work on the problem of structure had been done by other groups around the same time). It would perhaps be more correct to say that Franklin performed the experiments and Watson and Crick interpreted them in more detail (as Franklin's group also came to the conclusion that a double helix was responsible for some of DNA's shape).