Motorcraft SAE 75W-90 Synthetic Axle Lubricant. Recommended by bdcardinal here on BITOG. No idea how good it is, but nothing has made noise or blown up so far. :]
Valvoline Synpower 75W90
exclusively since the first change in the rear diff in my 07' Subaru WRX. Owned since new, changed the fluids early and the car has 134K and was modded out of warranty around 60K to run mid 13 second 1/4 mile times.
It has a pour point of -48C or -54 F.