The old standby of Velveeta and a can of Rotel tomatoes is hard to beat, but I wanted a something with a little more flavor. American cheese has developed a following on the net as the primary ingredient for queso. Here is one version.
1 1/2 lbs of white american cheese
2 cups of cream
2 tbsp ground chile
Molcajete salsa (optional)
Slowly heat cheese and cream, stirring frequently. When cheese is completely melted, stir in chile powder.
This has good flavor, but no heat. Add desired amount of Molcajete to get the heat you want.