These are just a few of many good OSINT collections online. Again, I've tried to keep it slimmed-down and simple - these include a lot of links to other collections, so feel free to go down the rabbit hole. If you want your collection featured here - or if you own one of these and want it removed - please let me know.
Bellingcat's Online Investigation Toolkit - Exhaustive listings of tools covering a broad range of aspects of online investigations
Financial crimes OSINT tools - Travis Birch's collection on money-laundering, banking and more
OSINT Combine bookmarks - A very comprehensive set of links you can download and import to your browser