High Voltage Resistors with tighter tolerances, but...
Murata Electronics North America has introduced the MHR03xx series of high voltage resistors that are available with tighter tolerances than previous versions. Tolerance is +/-0.5% up to 100MΩ, and 1% above that. Here'w what I like about their data sheet, found at http://www.murata.com/products/catalog/pdf/k99/k99e_l0055.pdf
The provide voltage rating in air, which they call "single use" and also when encapsulated. I like this spec a lot.
What I don't like, is that many specs are omitted. Like temperature coefficient and voltage coefficient. Perhaps they are shown in some other place on their website?