In Mexican restaurants they use queso blanco to make their cheese dip. Queso blanco is a cheese similar to queso fresco that becomes creamy when heated.
When used in a dip restaurants also use white American or Monterrey jack cheese as a substitute. They melt the cheese along with jalapenos, and diced chiles and serve it with tortilla chips.
A quick recipe uses 16oz of Queso Blanco Velveeta and 10oz of Rotel Diced Tomatoes & Green Chiles. Combine and microwave until melted.