The Y Combinator Database - The definitive database of YC companies with all the metrics
Startup Toolkit - Interactive how-to guides to launch your startup
Startup School - How to start a startup, by Y Combinator
Become an Indie Hacker - The ultimate resource for starting profitable side projects
Y Combinator Companies - Interactive list of all 1000+ YC companies
MakerMove - Discover great resources for makers and founders.