Harlan is a good teacher, for sure. Eric Jones is also very thorough when he does videos.
One that hasn't been mentioned is Wayne Houchin. His was one of the first lectures I attended and it taught me a lot about making good magic (not just how to do tricks).
Another - Ken Weber. Maximum Entertainment is probably one of the most educational books I own. Strong Magic is usually recommended right beside it, but I find Strong Magic to be a much more difficult read and honestly, it's just not quite as good (Still a book everyone should read, though, if they want to perform good magic).
Paul Brook's books are excellent. He really understands performance and mentalism on a level that most do not. Probably relates to his genuine psychology background.
Juan Tamariz's books are also quite good. It's been a while since I read them so I don't remember specific strong points, but I do remember a lot of "Aha!" moments reading the Five Points in Magic.
Oh, Eugene Burger, too. I only have two of his, but they both explain tricks and philosophy excellently (which makes sense, since he was a philosopher).
Aaron Fisher is a really good instructor as well. I have The Paper Engine and I've seen several of his videos. Very thorough explanation, without being overly repetitive.
And if you can find his books, and you can jive with his writing style, Derren Brown is also great. Again, more focus on the "Why" then the "how", which I appreciate.