For source material are you including material culture and artifacts? If you're only talking about textual pieces, its not even entirely post-Christian. Christian writers were perfectly willing to comment on the practices of these heathen societies and on the practices of their cultural cousins in places like England. I'm going to focus on textual evidence in case someone else more knowledgeable on material culture wants to chime in.

Many of the most famous descriptions of Norse activity come from Christian sources. The account of the great temple and human sacrifices at Uppsala come from the account of Adam of Bremen, a bishop from Hamburg. His perspective and motives in writing his account can hardly be considered objective.

The most famous examples of Norse mythology come invariably from the Icelandic Sagas, specifically the Poetic Edda and the stories that it contains. These stories are where we get almost the entirety of the surviving Norse myths and stories. These stories were complied and written in Iceland several centuries after the conversion to Christianity, so their utility in describing Norse beliefs prior to conversion is not ideal.

Furthermore, the sagas are Icelandic in origin, and while its certainly possible that wider stories and beleifs were tapped into in their composition, it cannot be verified. This is a problem because the beliefs and practices of the Norse living there, as remembered by a Christian population, might not necessarily hold true for Norsemen living in Kiev or Sweden.

Native Norse writing survived mostly in the form of runestones which do not go into any sort of detail on, well much of anything, but certainly not stories and myths. Some might argue that there was indeed native writing in runes, but no such manuscripts have survived to the modern day.

Other sources for Norse practices come from outside the Christian world though. The famous account of a viking funeral from Ibn-Fadlan's journeys in the lands of the Rus is a non-Christian perspective, but hardly a native heathen one. Ibn-Fadlan was a Muslim traveler and his account has been blended quite seamlessly into telling the practices of the Norse people, as if the scant evidence and accounts that we do have can be applied universally across the Norse world, which at its height spanned across the North Sea, into Russia, the Byzantine Empire, France, and as documented in the sagas, even North America for a short time.

The only source of indigenous information that comes from the Norse world is in the realm of material culture, artistic depictions, jewelry, burial practices, and so on. Unfortunately these sorts of sources cannot impart a great deal of understanding on what certain practices meant. Pendants in the shape of Thor's hammer can tell us that such charms were popular, but they cannot tell us if they were worn as amulets to ward off disease or other forms of evil, or because they were in fashion.