The PM Interview - Practice PM Interview Questions (w/ timer).
Y Combinator Companies - Interactive list of all 1000+ YC companies
Pramp for Product Managers - Practice product management mock interviews with other PMs
Apply to YC (Y Combinator) - Curated collection of resources for founders applying to YC.
Myskillwall - The best tool to prepare your job interview
Startup School - How to start a startup, by Y Combinator