1978 Yamaha 650 twin that was the vastly improved knock-off of the British twins. Still crude by today's standards, but absolutely bulletproof and gets 75 mpg!
Bought it new and still have it. Went through a lot of other bikes over the years, been riding since the early 60's, but could never part with the 650. When my Harley's were in the shop for the all too frequent rebuilds and the Wing's were too heavy for tooling around town, the old Yamaha would never miss a beat.
Now it is totally rebuilt with vastly improved progressive and re-valved suspension, Brembo brakes, clutch and control cable upgrade, manual fuel valves, carburetors brought up to the modern crap fuel standards and tuned, and old school off road handle bars similar to a Honda 450 Scrambler that I bought new as a kid - the Scrambler was junk though.
Crank it up, go for a spin, and it still puts a smile on my face!
Second is a Suzuki DRZ 400S. Light, fun, flexible, and economical, but completely disposable when its number is up!