The Stacks Project, an open-source textbook / knowledge repository on algebraic geometry, up to algebraic stacks and their theory. Cool idea, but I found it extremely terse.
A nice post on how memory constructs in Minecraft can be thought of as sheaves.
Some great notes on algebraic geometry from an introductory course at Cornell.
A nice textbook freely available online about algebraic curves (i.e. one-dimensional algebraic geometry) by William Fulton.
Some more great notes from an introductory course at TU Kaiserslautern.