Fatty fish like salmon are one of the richest natural sources of vitamin D. According to one source, a 100-gram serving of wild salmon can contain 556–924 IU of vitamin D, which is approximately 70–116% of the Daily Value (DV) for many adults.
Small, oily fish like sardines punch above their weight in vitamin D. While not as high as salmon, they still pack a significant amount. For example, canned sardines (in oil) contain about 193 IU per 100 grams, or about 24% of the daily requirement.
As a member of the fish family, mackerel also deserves its place. For example, according to the "Food Sources" table, 3 ounces (about 85 grams) of mackerel provides approximately 643 IU of vitamin D.
Eggs are convenient, economical, and versatile. The yolk contains most of the vitamin D. One source estimates that a whole egg (yolk contains vitamin D) contains 41 IU of vitamin D.
Mushrooms are one of the few non-animal sources of vitamin D (they produce vitamin D2 when exposed to ultraviolet light). However, whether mushrooms contain enough vitamin D depends on how they are grown/exposed. Some supermarket mushrooms contain very little vitamin D.
Vitamin D isn't naturally abundant in food, so many countries (and brands) fortify certain foods, including milk, soy milk, orange juice, and cereals. Here's a list: One cup of fortified 2% fat milk (US) contains 111 IU, about 14% of the daily value.
While oatmeal and yogurt generally don't provide as much vitamin D as fatty fish, they still provide vitamin D and have other nutritional benefits (protein, calcium). Cheese contains a small amount of vitamin D, according to one source (for example, one list states that 24 IU per 100 grams of cheddar cheese).
Eggs (a source of vitamin D), mushrooms (potential vitamin D if exposed/cured), and cheese (a little vitamin D and extra flavor) are combined in the same pan.