Bear in mind that in Northern Europe most written records we have were made by Christians significantly after the conversion of those regions so "good, accurate resources" may be essentially impossible to come across. Though it appears that a number of writers did have respect for their culture's pre-Christian roots, and took the trouble to compile information form sources no longer available to us, it may be "contaminated", as it were, by the Christianity of the writer. For Norse mythology, the best thing IMO is simply to read the Eddas. They are the largest coherent sources of Norse mythology available. The Prose Edda is a compendium of information that a Scandinavian skald (poet) would need to have known, mostly mythological in origin, written at some point in the 13th century by an Icelander named Snorri Sturlson. The Verse Edda is collection of poems, possibly compiled by the same fellow. If you're looking for something more cursory and readable, Myths of the Pagan North is a good read, but I always recommend the Eddas! Any of the sagas would be also a good place to start. For Welsh stories, check out any English translation of the Mabinogion.