Improving Software Usability?

kevin_conaway asks: "Software usability is one of the hardest things to get right. Writing good, usable software is the holy grail of software development, yet few developers give it more than an afterthought. As a professional developer, I delight in writing software for other developers but shy away from writing an interface that the end users will see. What resources/books are recommended for improving your Human Computer Interaction (HCI) / software usability skills?"