The Four Steps to the Epiphany - Steve Blank

The Art of the Start - Guy Kawasaki

Crossing The Chasm - Geoffrey Moore

Business Model Generation - Alex Osterwalder

The Personal MBA - Josh Kaufman

Blue Ocean Strategy - W. Chan Kim and Renée Mauborgne

Also, see:

http://www.quora.com/What-are-some-must-read-books-for-entre...

http://www.quora.com/Business-Books/What-business-books-must...

http://www.quora.com/What-are-3-books-you-would-suggest-any-...

and

http://personalmba.com/best-business-books/