Steve Krug covers many aspects of usability in an accessible, light-hearted and easy to read way.
It must be said, though, that Krug's idea of usability is usability for Americans. He assumes we all come from the same place, speak the same language, use the same language scripts and so on. He dismisses web forms in a couple of sentences and international web site users in even fewer. In terms of international viewers of web sites, some of his advice is downright damaging.
Read this as an introduction to usability, but look further too - otherwise we will never be rid of the scourge of the required "State" field in forms ...