Take The Bait - A blog about building your MVP & finding your first customer
Startup Toolkit - Interactive how-to guides to launch your startup
Launch Library - Hundreds of resources on how to launch literally anything
Techstars Entrepreneur's Toolkit - Online resource to help you learn about entrepreneurship
Lean Canvas - Business plans take too long to write, are seldom updated, and almost never read by others but documenting your hypotheses is key. Lean Canvas solves this problem using a 1-page business model.
AwesomeHunt - Community-curated lists of learning resources on any topic.