I was reading a question on here about the road to learning arithmetic geometry, and one of the suggestions was to start reading some foundational papers in the area. Similarly, one of the responses linked to a comment on Terry Tao's blog which echoed this view as a supplement to standard textbook treatments because it shows how these ideas get applied to problems.
Luckily, in this case many of the people pointed to papers, but I was wondering in general how to find 'foundational' (by which I don't nescessarily mean historically important papers, but papers which use the foundational techniques of a field) papers which might add more motivational material or context when starting to learn a field, as opposed to books?
