Low PPM Tc Resistors for Voltage Divider circuit?
Like Olin I was thinking of a resistor array. (Array being a big word for two resistors in a single package.) Firstly, being manufactured on the same process will give you a good matched value, and secondly being in the same package will make their temperatures also matching. At Vishay I found these "High Precision Thin Film Chip Resistor Arrays":  


  The networks provide 1 ppm/°C TCR tracking, a ratio tolerance as tight as 0.01 % and outstanding stability.  


edit
Linear Technology has the LT5400 resistor array with the following specs:  


  0.01% Matching
  0.2ppm/°C Matching Temperature Drift  


Prices start at USD 3.49 quantity 1000, so that's pretty steep. For a couple of resistors, that is.