Remote controlled cars/trucks for motors and power transistors.
I second this - these make great robot chassis if you BF is into that kind of thing; just make sure nothing is broken, and that the motors seem to rotate fine; spin the rear wheels and make sure you don't hear or feel any weird or abnormal grinding, also make sure the steering seems in good order (wiggle the wheels, let them go - they should return to center). If you can find an old R/C or wired-remote controlled tank (once again, check the treads/gearmotors for weird sounds, no binding, etc) - even better (they are difficult to find, though).
Another alternative is a Robosapien, or a RoboQuad toy.
Printers for stepper motors.
Definitely - also a great source of bearings and slide rods for custom CNC machines or robots; another great source for this are old scanners. Stay away from copy machines, though, unless they have removable toner cartridges - you don't want a toner mess! But they are also a great source for similar parts (same with fax machines).
Electronics from the 70's, 80's, and 90's will have more harvestable through-hole parts and fewer custom chips and surface-mount parts.
Be sure if you buy anything from the 70s or 80s that the device isn't considered an "antique" or "collectible" item; some old audio amplifiers from the era (and turntables, and tape decks, and you name it), as well as some computer components (and toys - speak n' spell, big trak, etc) - are -very- collectible; I've found at thrift stores and yard sales items going for nothing (I once bought an Atari Video Music for a buck!). The last thing you want is to tear something apart, and find out later that it was worth a lot of money (especially if the amount you spent on it was little to nothing).
This goes for computers, too: People are willing pay some big money for certain old machines (and old peripherals). It's becoming really difficult to find old 5.25" floppy drives (especially the low density ones - which usually had nice stepper motors in them) - people pay a lot of money for them today. And have you seen the prices people are asking for 386 motherboards? Especially the AMD 386 DX40 (that's a sweet ride there)... 486 motherboards are also going up in value. Apple IIe, C=64, Atari... If you ever run across an Apple Lisa you've hit the motherload...