Imperial Dry Neck Lube - don't forget to buy the little tub of "application media" too:
Imperial Lubricants | Redding Reloading Equipment: reloading equipment for rifles, handguns, pistols, revolvers and SAECO bullet casting equipment

It's dry, so no powder globbing up in the case mouth. Also, it's evenly distributed all around the inside of the case neck. Spray lube won't do that IME.

FWIW Imperial Sizing Wax works like a champ too - just don't use too much. I dab a finger in the wax every 2-4 cases and rub around the neck & shoulder every case. When you're done sizing, just lay the cases lengthwise in a row on a towel, fold it over the cases, and roll them clean.