There doesn't seem to be a lot of choices out there that are not dairy-based:
Substitute one of the following for each 1 cup of sour cream:
• For baking: 7/8 cup buttermilk or sour milk plus 3 tablespoons butter.
• For baking: 1 cup yogurt plus 1 teaspoon baking soda.
• For baking: 3/4 cup sour milk plus 1/3 cup butter.
• For baking: 3/4 cup buttermilk plus 1/3 cup butter.
• Cooked sauces: 1 cup yogurt plus 1 tablespoon flour plus 2 teaspoons water.
• Cooked sauces: 1 cup evaporated milk plus 1 tablespoon vinegar or lemon juice. Let stand 5 minutes to thicken.
• Dips: 1 cup yogurt (drain through a cheesecloth-lined sieve for 30 minutes in the refrigerator for a thicker texture).
• Dips: 1 cup cottage cheese plus 1/4 cup yogurt or buttermilk, briefly whirled in a blender.
• Dips: 6 ounces cream cheese plus 3 tablespoons milk, briefly whirled in a blender.
• Lower fat: 1 cup low-fat cottage cheese plus 1 tablespoon lemon juice plus 2 tablespoons skim milk, whipped until smooth in a blender.
• Lower fat: 1 can chilled evaporated milk whipped with 1 teaspoon lemon juice.
"God gave you your body as a gift, so you should take care of it." - My Mom