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