I'd like to add two people that have at times fundementally changed my jiu jitsu, and I will go out of my way if possible to train with, they're that awesome
This forums own Aaron Lapointe. I'm privileged in that we're teammates and he's a good friend of our academies, that being said his seminars etc are fantastic, he's a great teacher and has amazing jiu jitsu, and focuses a lot on concepts not just foot here, hand there stuff, I first trained with Aaron as a white belt and his concepts of control (head, hooks/hips, grips) resonated and is a fundamental part of my game. (I'll let him explain in this or another thread if he sees) I've never trained with him and not taken something away that can immediately be used. If you get a chance by all means do yourself a favor and train with Aaron, he has a fantastic and inspirational story, can't say enough good things, a great human.
Hannette Staack, 100% changed my game, amazing teacher, amazing jiu jitsu. Again I would go out of my way to train with her. For all my training partners who laughingly bemoan my passing as especially side control pressure and think it's because I modeled myself after wallid (partially true) it's mainly hannette, she (and my instructor Goatfury) changed the way I approach passing in general and side control in particular (amongst other things) she's fantastic and a great person