Keithley 2182A 

Digital Nanovoltmeter & Low Voltage Meter
Make low noise measurements at high speeds, typically just 15nV p-p noise at 1s response time, 40-50nV p-p noise at 60ms
Delta mode coordinates measurements with a reversing current source at up to 24Hz with 30nV p-p noise (typical) for one reading
Synchronization to line provides 110dB NMRR and minimizes the effect of AC common-mode currents.
Dual channels support measuring voltage, temperature, or the ratio of an unknown resistance to a reference resistor.
Built-in thermocouple linearization and cold junction compensation.
Averages multiple readings for greater noise reduction