Besides that their book "Getting Real" can be bought in PDF or printed copy, people from 37signals decided to publish it online. You can read it absolutely free from your browser. Just type http://gettingreal.37signals.com/ in your browser for front page or http://gettingreal.37signals.com/toc.php for Table of Contents.
As small reminder, here is part of author's description of this book:
What is Getting Real?
Want to build a successful web app? Then it's time to Get Real. Getting Real is a smaller, faster, better way to build software...