My answer is...a catalog.
The internet makes it easy to find something, but knowing what to find, having those holistic, framework-sized grasp, is hard without exposure to something as rigorously organized and easy to flip through as a catalog.
Flipping through a Uline or Demco catalog will blow your mind. Some of this stuff has been invented 50 years and you have no idea. Wish I could link to some good examples but am on mobile / trust me on this, the catalogs are free after all.