Answers.OnStartups: Q&A site for entrepreneurs looking to start or run a new business
Stanford eCorner: This site has tons of resources, including a great structure for your entrepreneurial pitch/plan (Guy Kawasaki video)
VentureBeat: Entrepreneur Corner is where VentureBeat collects advice, how-tos, case studies and other useful, actionable business information for startup companies and the entrepreneurs who are behind them.
The Four Steps to the Epiphany, Steve Blank
Lean Startup, Eric Ries