More of a tool than something technical, but this thing was passed down to me after my father went to the playground in the sky and has to be at least 25 years old. I've never even replaced the tip, just file it down now and then to retin the tip.

Another great tool (that also passed down to me, and is also similarly about 25 years old) is a Beckman Industrial DMM. I've used it extensively in projects indoor and outdoor and I would put it up against a Fluke for quality and accuracy. I love that two of my staples when it comes to tinkering have been so dependable over the years.