Like in anything, the most successful are not usually the best teachers or the most knowledgable. The best pro golfers listen to guru teaching pros who have fairly limited competitive success on their own. Some of the best strength and conditioning coaches in the world are marginal athletes when compared to those whom they are coaching.
A long time ago I took a PT job in a gym for some summer money where one of the trainers was a bodybuilder (he earned his Pro card about 6 months later). We were talking one day and I asked him about his training and routines. His answer was "I do X sets for arms, Y sets for legs, Z sets for chest...." Right then I knew this guy didn't know anything more than the other noodlearms at the gym. It was drugs, diet, genetics and admittedly hard work but without the drugs he'd be just another guy running around wondering why he couldn't get bigger. His clients made little progress while every one of mine (even the slackers) was making very consistent month to month progress and more importantly felt self empowered in that they knew what needed to be done and were able to make progress under their own power (improves your whole outlook in life when you are out accomplishing a goal and making yourself better).
Most people would look at this guy and look at me and choose him to train them any day. Then again, people who know what to look for would watch us both train - me doing cleans/snatches/pulls, a variety of squats and him doing leg presses, cables, machines, and BS isolation exercises training to failure - they'd know the truth instantly.
EDIT: Anyway, people I listen to (authors/coaches/etc...not an exclusive list - just some names that come to mind):
L. Simmons (WSBarbell)
D. Tate (WSBarbell)
G. Pendlay (IMO - one of the best strength coaches on the planet)
B. Starr (One of the best strength coaches ever. Only the Strong Shall Survive - out of print, always loved reading his reprinted articles which where the only redeeming quality to the trash magazines in which they appeared)
Medvedyev (researcher/author)
Zatsiorsky (researcher/author)
Siff (author)
Laputin (researcher/author)
Roman (researcher/author)
Verkhoshansky (researcher/author)
Some Good Readings:
www.elitefts.com - Go to the books on training. You'll find the following (in no particular order):
A System of Multi Year Training in Weightlifting
Bigger Fast Stronger
Fundmentals of Special Strength Training in Sport
Supertraining (plus lots of others by Siff)
Managing the Training of Weightlifters
Science and Practice of Strength Training
http://www.dynamic-eleiko.com/ - Go to Products, Sportivny Press Weightlifting Texts - Russian Weightlifting Library
Here you'll find a number of translations from the above authors that are not available in Enligsh from anywhere else that I've found.
http://www.deepsquatter.com/strength/archives/index.htm
Nice collection of articles - excellent read.
Some good discussion boards (I'm sure there are others too but these are some of the ones I tend to read on occasion if I'm feeling inclined):
www.fortifiediron.com - some knowledgable people specifically in PLing, OLing, and Track and Field.
www.mesomorphosis.com - their training board has a few people that are really great, particularly Johnsmith182 - be sure to check out the stickies and his tribute sticky in the training forum.
www.goheavy.com - probably the best OLing forum on the internet with more coaching depth than anywhere else. Glenn Pendlay is a mod here.