When Steampunk as a literary movement is discussed, there is invariably the necessary mention of the proto-Steampunk authors whose past works shape literary Steampunk today. Usually, discussion of these early authors starts and ends with Jules Verne and H. G. Wells, but there are far more authors that were doing similar work around the same time which influences Steampunk.
Verne and Wells enjoy particular respect within the Steampunk community not only because they wrote some of the greatest works of science fiction literature of all time, but also because much of the Steampunk community has read their work.
The article The Birth of Steampunk in the 19th Century by Jess Nevins is a reading list for those interested in expanding their familiarity with the proto-Steampunk authors beyond Verne and Wells. It offers reading suggestions in chronological order by publication date along with links to read many of the referenced works for free.
This list is a great way to expand your knowledge on the science fiction that would eventually come to shape our subculture.