Highly acidic.
Use only on oily skin and use in moderation:

Lemon*
Grapefruit*
Apples*
Strawberries*
Lime*

Slightly more acidic than normal skin.
Beneficial for most skin types:

Peaches*
Apricots*
Tomatoes*
Grapes (not Concord)*

Neutral.
Beneficial for most skin types:

Cucumber*
Bananas*
Watermelon*
Persimmon*
Pepper*

Low acidity.
Good for moisturizing dry skin:

Carrots*
Cantaloupe*
Avocado*
Honeydew Melon*
Iceberg Lettuce*

NOTE: Facial masks should be applied very gently to preserve the cusion of fatty tissue and avoid stretching the surface skin.

Be sure to test a small area for skin sensitivity before using any mixture on your face. Dab a little on the inside of your wrist or the underside of your arm and wait a 24-48 hours to see if it causes a reaction, such as a rash.

Mayonnaise?
Yes, simple mayonnaise contains many useful skin nutrients. Use your own recipe (but leave out the salt!), or buy a good salt-free mayonnaise and massage it into your skin as a night cream.

Bran and Oatmeal
Bran and oatmeal both make great hand smoothers. To make bran water, add 1 cup of boiling water to 1/2 cup of natural bran and allow to steep for 15 minutes. Strain out the bran and leave small amount of bran water in a bowl by the kitchen sink (refrigerate the rest until you're ready to use it). Dip your hands into the water and dab them dry 3-4 times a day, especially after washing dishes.

For an oatmeal wash, simmer one part of old-fashioned (non-instant) oatmeal in 2-3 parts water until the meal swells and is soft. Strain into a container and use like the bran water.