Cognitive bias cheat sheet – a comprehensive overview of the different types of behavioral biases grouped by category
Magic Formula Investing – Joel Greenblatt’s free screening site that uses his work that shows that stocks that rank well on both Return on Invested Capital (ROIC) and cheapness do much better than the market over time.
Value Investors Club – A free membership-only idea exchange site for value investors. Non-members can read content for free on a delayed basis.
Manual of Ideas – An excellent publication for generating new investment ideas as well as improving your thought process by reading or watching interviews with thoughtful value investors.