For me, it was Seth Godin. His first book, Permission Marketing, was a business book... it taught me a lot, but more than anything it led me down a path.
I read many of his other books - The Dip, Tribes, Purple Cow. Then I was hooked, and I moved into other self-improvement works: Tim Ferriss, Tony Robbins, and many more besides. For me, these books were a source of motivation and inspiration. It may be silly, there may be platitudes... but for me, it really worked.