Eric Coates provides lesson modules for a range of electronics sub-topics. Including: digital electronics, circuits & resistors, AC theory, amplifiers, oscillators and so on.
Tony R. Kuphaldt provides a range of useful resources on the topic of industrial instrumentation. Including a link to his textbook which is constantly being updated and improved (make sure you use the 'stable' version). There are also some interesting examples of what 'not to do!'.
