This is a tough cut but I will offer you some titles that have been the most useful to me. I do enjoy a good fishing story when combined with some technique but the books listed below were the real workhorse reads that helped me climb my own personal mountain.
When I needed to have a large volume of nuts & bolts how to information, Tom McNally put 'Fly Fishing by Tom McNally'
out. It was simple to understand and could be taken from theory to practice quickly. This was a most helpful work and I can't imagine getting over the learning hump without it. His casting, knots, and basic water sense are hard to improve upon.
I bought many books but none could offer anything more than McNally had delivered until my fishing buddy gave me 'Advanced Fly Fishing For Steelhead by Deke Meyer'
in 1993. I had been thrashing around the Great Lakes rivers and creeks after these fish and although the book was primarily dealing with West Coast fishing conditions I found some good kernels of info there as well as some fly patterns. It was very nicely done, I know there are many books about steelhead but this is the one I have and I got it just for being me.
A few years back I moved from relying on old wives tales for understanding salmon and I found 'The Behavior and Ecology of Pacific Salmon & Trout by Thomas P. Quinn'
to be very informative and useful in establishing an understanding of these species.
In the 90's a similar book 'Trout' one of 'The Wildlife Series'
was a collection of research edited by Judith Stolz & Judith Schnell was another gift from a second fishing friend. This proved to be a most mind altering work to have on hand, some things you thought you knew were shown to be true and many things you hadn't ever entertained the thought of were disclosed. The book deals with every species of trout on our continent and their behavior and environmental needs and constraints. A very good book for anyone looking to understand trout as a species.
Last but not the least was Nick Karas's book 'Brook Trout'
Here Karas takes you on a historical study of Salvelinus fontinalis from the Wisconsin period ice age to contemporary times. If you enjoy the Brook Trout and want to know about its history, biology, ecological challenges and range, this is a must have work.