I have been recently re-reading all of the Leonard Wright books in my bookcase, which has me in a Catskills sort of mind. Yesterday I pulled out The Complete FlyFisherman - Notes and Letters of Theodore Gordon, edited by John McDonald. Before I am done with this strain of interest, I am sure that I will have re-read everything within reach concerning the Catskills.
If you can find a copy of "In the Catskills," a collection of essays by John Burroughs, I recommend you get it. It's theme is not particularly trout fishing, but natural history and rural life, and very enjoyable nonetheless.