I've been a fan of this website for ages. What I like is the no-nonsense approach and referring to the underlying mechanical principles.

Cycles are an interesting invention as it's easy to look at and figure out what the parts are doing and this leads to a huge number of people thinking that they can improve certain bits. Unfortunately, most "improvements" aren't and there's very good reasons why cycles have evolved to their modern designs. In engineering terms, I find it fascinating as cycles are all about trade-offs e.g. strength/weight/aerodynamics/cost