Cultured or fermented dairy products like yogurt and cheese contain the least amount of lactose because the culturing process pre-digests much of the lactose. Also, as whey is removed from a dairy product during processing, such as in cheesemaking, much of the lactose is removed along with it.
As such, hard, aged cheeses are among the lowest lactose dairy foods. These include cheddar, parmesan, Swiss and other "block" cheeses. Dairy foods that have lactase enzyme added to them, like our lactose-free yogurt, kefir, sour cream and cream cheese, are also completely lactose free.
Butter is also very low in lactose, as it is primarily composed of fat rather than lactose-containing milk solids. Softer cheeses, cottage cheese and conventional yogurt are moderate in lactose, and may be tolerated by some people with milder forms of lactose intolerance or in small portions.