In addition to some of the people already mentioned above (Werner, Murphy, Langdon, Douglas), I took a one day class last year with Tatiana Whitlock, and I thought she did a great job. It was an interesting class not very much like other pistol classes I've done, with some unusual things like her "take a chair" lesson and her "yoga with guns" bit, as well as an introductory drill that was kind of mentally painful but very worthwhile.
I'd also say that the OP asked about quality trainers, and while that leads to a natural tendency to mention the best nationally-known folks, I would also say that there are likely to be good people teaching at a more local or regional level. I took a class last year with Defensive Concepts NC, and while the instructor swore more than any man I've ever met, the class was a great value, and the instruction was very good. I just took an Ernest Langdon class that was hosted by a guy who runs a local training company called Fortitude Consulting. He's one of Jedlinski's endorsed red dot instructors. I stood next to him on the line for three days and asked him a couple of questions. While I have not trained with him and hence cannot actually say that his training classes are great (or otherwise), I personally wouldn't hesitate to sign up for one of his classes, based on my experience of him, and my knowledge of his training background and experience. There are other such companies I could mention.
I spent a few years wanting to take a pistol training class but not doing it because of expense, travel, etc, because I was focused on finding a national trainer. Once I went with a local guy, I found a one-day, affordable class in my own town, and that got me going. So I'm a fan of local trainers, just as long as you intelligently vet them ahead of time.