As I've been toying with the idea of grad school, I've done some reading in the field of literary theory over the past few weeks. Two books I've found both helpful and enjoyable:
Critical Theory Today by Lois Tyson
From the back cover: "Critical Theory Today is the essential introduction to contemporary critical theory. It provides clear, simple explanations and concrete examples of complex concepts, making a wide variety of commonly used critical theories accessible to novices without sacrificing any theoretical rigor or thoroughness." This is probably the most helpful book I could have read--a genuinely interesting refresher.
Six Walks in the Fictional Woods by Umberto Eco
From the back cover: "We see, hear, and feel Umberto Eco, the passionate reader who has gotten lost over and over again in the woods, loved it, and come back to tell the tale... Eco tells us how fiction works, and he also tells us why we love fiction so much." This book is a series of lectures given by Eco on how authors write and how we read. Although the first chapter was a bit esoteric for my taste, Eco's genial humor and incredibly wide-ranging taste in reading matter made this short book a fun read.