A book that simply has not been receiving the amount of attention it deserves is Domain-Driven Design by Eric Evans (a friend of mine). This book does an excellent job of taking the most powerful object-oriented practice so far, domain modeling, and explains it with what is probably the most revolutionary documentation technique of at least the past decade, patterns. The result is a book that describes exactly how to develop the domain model your application needs. As Kent Beck commented, "The book is absolutely fabulous! I wish I had written it."
There's now an article by Jimmy Nilsson (another friend), "Simplify Your Efforts With DDD." In it, Jimmy captures the essance of Eric's book and techniques (in a nutshell, as it were) and illustrates why it's so useful. Give it a read and find out what you're missing.
For more thoughts on books you might want to check out, see my recent post ISSW Recommended Reading List.