R.P. Agarwal & Said R. Grace 
Oscillation Theory for Second Order Linear, Half-Linear, Superlinear and Sublinear Dynamic Equations [PDF ebook] 

In this monograph, the authors present a compact, thorough, systematic, and self-contained oscillation theory for linear, half-linear, superlinear, and sublinear second-order ordinary differential equations. An important feature of this monograph is the illustration of several results with examples of current interest. This book will stimulate further research into oscillation theory.This book is written at a graduate level, and is intended for university libraries, graduate students, and researchers working in the field of ordinary differential equations.