I use Breakfree CLP - it cleans and oils.
I believe the military uses it for their M16s.
I've seen several tests. Its one of the top 2 or 3 in preventing rust in tests, and someone on the Sig Forum did a freezing test last week - it resisted freezing as well.
I've used it for years. U can buy the aeresol can at Wal-Mart, but I prefer the liquid in a bottle over the spray can.