"Different" by Youngme Moon. This book was given out at the Business of Software 2010 conference, and she also spoke there. It's basically a call to arms for meaningful differentiation with organized business case studies of companies that have achieved it.

http://www.amazon.com/Different-Escaping-Competitive-Youngme...

Love Made to Stick and Founders at Work. I haven't read 22 Immutable Laws of Marketing, but I'll check it out, thanks.

One excellent marketing book I recently read is Different: Escaping the Competitive Herd by Youngme Moon (no ref link: http://www.amazon.com/Different-Escaping-Competitive-Youngme...). She believes that going tit-for-tat on adding features and augmentations is a losing game that results in every competitor looking like one another. Instead, you should find your strength, and focus on that while resisting to focus on where your product falls short. The book is also very... poetic. She's quite a quotable writer. Good stuff.