It's been two years since the second edition of Steve Krug's “Don't Make Me Think” was released. Several other books on Usability have been published since. But for my money, “Don't Make Me Think” remains the best primer available.
Certain other authors delight in making the process of improving usability appear as complicated as possible. It's an age-old trick: inflate weak ideas by propping them up with quasi-academic language and unnecessary jargon. Steve Krug – whose corporate motto is “It's not rocket surgery” – takes the exact opposite approach. He explains, in everyday language and with vivid examples and analogies, how achieving good usability is largely a matter of common sense.
If you're looking for a highly readable, witty, insightful and actionable guide to improving website usability, “Don't Make Me Think” is, in my opinion, your best bet. You can buy the book here: Don't Make Me Think
No, I don't get royalties. I'm just a fan… of Steve Krug, and of common sense.