Jim Clark's Models for Ecological Data (aka The Elephant Book) is a really badass book. It is also a not the easiest read. I managed to slog through chapter 7 last summer in about 4 hours. This summer I'm going for the whole thing.
How to do Ecology is short, practical and well written. I've heard some of the big guns in ecology read it once per year.
During the summer, I spend a lot of time in the woods. I don't want to die in them, so I figure I should read this.