Favorite publisher goes to Cubicle 7.
This due to my sometimes unfortunate completion-ist way of collecting the games I get into and the wonderful quality of the products. A good majority of the books I've purchased in the last several years are from a few lines produced by Cubicle 7. This started with the Doctor Who RPG. I tried to resist the sourcebooks. But apparently not too much. These are wonderful. They system is simple and crunchy enough, the layout is quite professional.
I also have been collecting The One Ring books. The production quality of these books are so very fitting with the setting that it adds to the immersion of Middle Earth greatly. The care that went into the layout and artwork for all of it so far feels like a real labor of love. It is this quality that gives me a great deal of trust to Cubicle 7.
Second goes to Fantasy Flights' Star Wars games. The greatest strength in these books is the decision to not use images from any of the films or shows. All the artwork is original and for the most part, pretty darn good.
Lastly, I have been very impressed with Pinnacle's new hard cover book format. I do look forward to more of those on my shelves. In the shape and size of comic books and graphic novels, these are turning out to be very nice.
We live in a remarkable age of quality for this hobby.