Heathkits

[Fisherdude]

Heathkit was in business for many years, probably from the '40's thru the early '80's. The company, or at least its current survivor, is still in business making electronic training materials for classrooms. They haven't done kits in decades. Look here:
http://www.heathkit-museum.com/history.shtml

They made just about everything, from test equipment, hi-fi gear, shortwave and ham radio transmitters and receivers, to kid's stuff like science fair kits, etc.

Difficulty level ranged from very simple to kits that were clearly intended for very experienced electronics builders.

eBay has thousands of pieces of Heath equipment. However, it's all built! If you're looking for an unbuilt kit, they do pop up from time to time, but they will be very expensive.