I confess, I only have crappy meters. But I often have the need to calibrate ADC measurement, and I would like to calibrate my meters so they are all in the same ballpark. So I have built myself a simple, cheap, and reasonably accurate reference. It is based on a ADR510 voltage reference. According to the specs it is 1V +/- 3.5mV, 70ppm/C.
And I had some boards made from OSHpark
Checking it with my crappy meters, it appears to work.
(edit: I replaced images of board with renders due to embarrassing spelling errors)