Flat Seat adjustment aka the fisheye dart from the Sewing Space (video tutorial)
Colette’s Cheatsheet for pants fitting. Not all go to tutorials but I’m guessing more are in the works.
Of note, Colette has up a pictutorial for both flat and full butt. Start with the butt and crotch.
Sewaholic pants fitting resource links (but really, it’s the same Colette and Sunni links)
A Fix for a Baggy Seat by Kenneth D. King
Madalynne talks about crotch hook width
If I’m missing a really great online fitting tutorial please let me know. I’m looking for all kinds of fitting instructions but specifically how to fit slim fit/skinny pants/trousers/jeans.