This page has some great stuff on custom magic items, and other articles on monsters and such that are great flavor, and I’m probably going to end up swiping.
Of course, the original blog that inspired me to write my own. They have a ton of great articles.
One of my favorite go to forums to get questions answered, or to just join in conversations being had.
This site has several great articles on encounters, thematic combat, and other assorted information that I’ve found really useful
I’ll add more as time goes on. Enjoy!
Enworld has a lot of good fan made material as well.