This dip was a huge hit at my office potluck, it tastes just like a Reuben sandwich, minus the bread. I made it up the night before and put it in the fridge. The next morning when I got to work I plugged in my Crock-Pot and it was ready by lunch time!
In a mixing bowl, beat the cream cheese, sour cream, and 1000 Island dressing. Add the corned beef, sauerkraut, Swiss cheese, and onions.
Dump the mixture into the Crock Pot.
Cook on low for 2-3 hours.