Reddit mentions of Heimskringla: History of the Kings of Norway

I understand this. Some relevant links in Norwegian:
University of Oslo on how Christianity came to Norway

Here an article on the first Christian inscriptions in Norway from University of Technology and Science in Trondheim

Both the above articles refer to the fundamental academic book on early Christian influence in Norway: Fritjof Birekli Tolv vintre hadde kristendommen vært i Norge = Christianity had been 12 winters in the country

Snorri Sturlassons books on Norse mythology as well as on king Haakon the Good and other early Norwegian kings are available in English. His books are fundamental sources for an understanding of the Norse universe of thoughts for the twelfth century when they were written - and is what OP is looking for

>I couldn't recommend translations for either of these to English, as I've read them in Norwegian translations.

I have this edition of the Heimskringla and this of Egil's saga and found them both to be pretty solid and readable. The Penguin edition of Njal's saga is also pretty good.

The best FREE online source (http://www.sacred-texts.com/neu/ice/)

The most important works on the subject are the EDDAS, the poetic and prose and your collection cannot be called complete without them (http://www.amazon.ca/The-Prose-Edda-Mythology-Classics-ebook/dp/B002RI9HRU/ref=pd_sim_kinc_8?ie=UTF8&refRID=0M032MEETG0CVXAT539W) (http://www.amazon.ca/Poetic-Edda-Oxford-Worlds-Classics-ebook/dp/B00LKGBK1Q/ref=pd_sim_kinc_1?ie=UTF8&refRID=1CGS5F6Q2WWB3HR2DKFR)

Sagas of the Icelanders is a pretty comprehensive book and an easier than scholarly text read (http://www.amazon.ca/Sagas-Icelanders-Penguin-Classics-Deluxe/dp/0141000031/ref=sr_1_1?s=books&ie=UTF8&qid=1425947217&sr=1-1&keywords=sagas+of+the+icelanders)

A great historical (a little mythology) view of the Vikings in John Clements the Vikings (http://www.amazon.ca/Brief-History-Vikings-Jonathan-Clements-ebook/dp/B00AJN9KHC/ref=sr_1_fkmr0_1?s=digital-text&ie=UTF8&qid=1425947425&sr=1-1-fkmr0&keywords=the+vikings+john+clements)

A great dictionary/listing of Viking myths can be found in Cassell's Dictionary of Norse Myth & Legend (http://www.amazon.ca/Cassells-Dictionary-Norse-Myth-Legend/dp/0304363855/ref=sr_1_cc_8?s=aps&ie=UTF8&qid=1425947500&sr=1-8-catcorr&keywords=dictionary+of+norse+myths+and+legend)

A great source for the kings of Norway and their (mis)adventuires would be the Heimskringla but there isn't as much mythology in there, more historical (http://www.amazon.ca/Heimskringla-History-Norway-Snorri-Sturluson/dp/0292730616/ref=sr_1_1?s=books&ie=UTF8&qid=1425947617&sr=1-1&keywords=heimskringla)

There's a bunch of other sagas you may want to sink your teeth into: Njal's, Grettir's, etc... If you want to listen about some Viking sagas via podcast, I'd recommend Saga thing, both entertaining and informative (https://sagathingpodcast.wordpress.com/)

Thanks for the help, everyone, but I've found one that I'm going to buy!

http://www.amazon.com/Heimskringla-History-Norway-Snorri-Sturluson/dp/0292730616