The tautology about popular mythology is that that there’s a lot of information about popular myths because they’re popular.
But here are some reasonable resources that have other cultures represented:
Encyclopedia Mythica: Pretty much exactly what it sounds like, with Inca, Latvian, and Aboriginal myths represented right along with Greek, Roman, and Egyptian myths, among others.
Folklore and Mythology Texts: Sorted by type of myth (bald myths, hauntings by ghosts of murdered children, Three Little Pigs, changelings, etc), this website reproduces original texts and sometimes includes a small explanation.
Godchecker: We have posted a link to this website before, but a lot of this information is biased and better used as a starting point for further research rather than a definitive source.
Superpower wiki: Another previously posted link. While superheroes are not strictly mythology, they are certainly a part of modern folklore, and originate from the same vein as classic mythology, and I thought it would be worth including.
Fuck Yeah Celtic Mythology: A tumblr with pretty well-sourced posts, with links to original texts and also lots of Celtic art. Obviously just Celtic mythology.
Fantastical Lore: A tumblr with a lot of varied mythology, but is no longer updating frequently.
Deities Daily: Hasn’t posted for a while, but has some semi-obscure myths.
Mythology Curator: “Like tracking the mythology tag, but better.” An accurate statement. Some good info, but also a lot of colorful commentary.
All About Myths: Beautiful fan art reblogs and helpful information, including some bits that popular myths leave out of their own stories.
Fuck Yeah Strange Mythology: Not necessarily “strange” mythology (although, isn’t all mythology a little strange?), but a lot of uncommon myths reblogged here.