First off when you say Germanic that can be interpreted to mean a very specific geo-physical region during a specific time, or sometimes gets used for the whole umbrella. I'm assuming the later based on the rest of your post.
I personally feel that over 90% of it is never read or looked at within the community at large. Most never bother to read anything beyond the Eddas. To be fair, we don't all need to be scholars with academic backgrounds. But it does help us try to glean things out while we try to reconstruct things.
The more popularly read (within our religious community) Eddas, and sometimes assorted Sagas. Often overlooked are the various bits of Skaldic poetry, and it's a pity they tend to be overlooked as we know that around 30 of these skalds were either heathen or converted in their lifetime. Downside is their work tends not to have the 'myths' that many are looking for to understand our Gods. But you can still glean some insights. Don't forget the various legal codes too: Guta lag, Gragas, Frostathing Law, etc. Also the various chronicles, like the Anglo-Saxon Chronicle.
MERSEBURG CHARMS
The Merseburg Charms (only remaining evidence of Germanic pagan belief written in the Germanic language). The first one talks about the Idis (Matronae, Disir). the second one has the horse healing charm where Baldr's horse is healed by Odin, Frigg, Fulla, Sunna and Sinthgunt.
Roman and Byzantium Scholars & Historians
Pliny's Historia Naturalis, Julius Caesar's Commentarii de bello Gallico, Sidonius's Letters, Tacitus' Germania, Strabo's Geographica, Jordanes' Gettica, etc. (Keep in mind some of the authors have multiple items of interest too). Plus Byzantium scholars like Ionnes Scylitzes (aka John Skylitzes). Thru him we know that among the defeated Varangians at the Siege of Dorostolon in 971, a number of armed women were found among the slain, much to the shock of the victorious Byzantine forces. The Byzantium scholar Procopius wrote the History of the Gothic War. I always appreciated the tale of an unnamed Anglian princess that led a fleet of 400 ships against King Radigis of Jutland. There's more references across Roman and Byzantium sources too of course.
Arab, Middle Eastern & Jewish Accounts
Usually from those who hailed from the Cordoba or Abbasid Caliphates, but some other accounts from that world. Usually these were diplomats or merchants who wrote of their travels, or there interactions. This is where we get Ibn Fadlan who visited the Kievian Rus. We have Al-Tartuschi (aka Ibrahim ibn Yaqub) who spoke of witnessing religious ritual in Hedeby, Denmark. I know there's over 15 such accounts/authors. Ibn Battuta and Al-Masudi also. I've been slowly trying to track them down, English translations for some of them are scarce (possibly non-existent, so then I try to see if there have a translation in a language I at least have some reading comprehension in). But keep in mind the sources are not only about what we're interested in. Like even Ibn Fadlan's commentary on the Rus is only a few pages out of a lot of writing. In some cases the original sources are lost and all we have are excerpts quoted by other scholars from antiquity. Dunlop's History of the Jewish Khazars has some relevant content too as he aggregates from several of those period sources.
EUROPEAN CHURCH DOCUMENTS & CHRONICLES
I'm defining this as both sources written by Church figures, but also by scholars attached to the political courts of Christian rulers.
A shit ton of Church documents, a lot of these may be hagiogrqphies on the lives of the saints (example Rimbert's Vita Ansgari). But they're worth mentioning. As you find stories about the ways Christianity tried to eradicate the pre-Christian religions. This tends to be a blind spot of mine, cause I hate reading biased hagiographic texts that hype the saints. But accounts like that are where we have the tale of King Radbod deciding not to convert because he'd be separated from his ancestors. So there are gleanings in them too. We also have soures often times meant to be chronicles or histories like venerable Bede and his works here too (Historia ecclesiastica gentis Anglorum, De temporum rationae), a key resource for what was going on with Anglo-Saxon areas. Adam of Bremen'Gesta Hammaburgensis Ecclesiae Pontificum, Paul the Deacon's Historia Langobardorum, Saxo Grammaticus' Gesta Danorum. Etc. Technically by my definition of this category, Snorri and his Prose Edda should fall here too as he was Christian attached to a Christian court, and the Anglo-Saxon Chronicle too.
FOLKLORIC
Jacob Grimm's Teutonic Mythology is one of the key touchstones here. But there's a lot of other folklorists too. Typically you're looking at a period from the late 1700s through the early 1900s when this content was first intentionally penned down. Most are in their native European tongues and as such most do not have direct English translations available. Rudolf Simek's Dictionary of Northern Mythology will sometimes list various bits of known folklore among some of the entries pulled from various sources.
MISCELLANEOUS
Runic poems, the Anglo-Saxon Charms (Nine Herbs, the Æcerbot, etc.)
ARCHAEOLGY
Settlements, Grave Goods, Pollen Analysis, DNA analysis, Metallurgic analysis, jewelry, amulets, votive stones, tapestries, etc. Dubois' Nordic Religions in the Viking Age gives a summary overview and a handy map which shows us the reach during the Viking Age. Remember during the Viking Age we see Scandinavian Migration and trade networks, with settlements that spread from what we associated in the modern day with Canada to as far east as Russia, Northern Europe down to North Africa and the middle east. We see settlements along the costs of the Caspian Sea, Black Sea, Mediterranean, north Atlantic and Norwegian sea. Plus Viking raids as well.