Sour Cream:

Lime-cilantro, stir in a handful of fresh cilantro and the juice of 1 lime.  Serve with tacos or fried fish.
Brown Sugar, which in 2 tbsp. brown sugar and a dash of cinnamon.  Serve with fresh strawberries or bananas for dipping.
Ketchup, chili-lime stir in 1 minced chipotle pepper in adobo sauce and the juice of ½ a lime.  Spread on beef or turkey burgers.
Maple BBQ, stir in 2 tbsp. maple syrup and a few dashes of Worcestershire sauce.  Serve with chicken fingers or French fries.
Mustard, whisk in 2 tbsp chopped fresh parsley and 1 tsp. each minced thyme and rosemary.  Serve with grilled steak.
Sweet citrus, stir in 3 Tbs. orange marmalade and a sprinkle of red pepper flakes.  Serve with grilled chicken or salmon.
Raspberry, purée with ½ cup raspberries and a spoonful of honey until smooth.  Spread on ham or turkey sandwiches.