One of my favourite books..
Yes, Phil Gordon's Little Green book is one of my favourites....it helped me step up my aggressive game because it taught me when and how to do it.
It gives a good breakdown of categorizing different players and then how to be aggressive or not against them.
Also I liked his examples sprinkled in the book of how much he would raise with various hands and why he would raise that amount or why he would raise in the first place.
I recently lent it to someone...and just realized I should ask for it back because I often refer to it when I'm waiting somewhere and have brought it with me to read.