Disclaimer: this post is geared primarily towards historical-fiction writers, specifically those writing about classical antiquity-apologies for the narrow scope! 
I’ve started putting together a master post of the most helpful online resources I’ve found in doing research for my Cymeria series, in the hopes that somewhere, somehow, someone else might also find them useful.
I’ll probably keep adding to this list as time goes on and I dig up more stuff. I’m always on the lookout for new sources, particularly if they’re on topics that don’t get a lot of attention, so feel free to comment with suggestions and additions!