I've made this recipe for pickled green tomatoes from Splendid Table; it's pretty good. If you've got grape tomatoes, though, you should definitely make tomolives:
Pack the tomatoes snugly into a jar. Add 4 cloves garlic and a tsp of pickling spice. Bring ¼ c. salt, a pint of Heinz white pickling vinegar, and a pint of water to a boil. Pour over tomatoes, let cool, and store in the fridge. The Temple Bar in Manhattan served an "old South martini," garnished with tomolives, which is where I first had them. They're also great in bloody marys.
I made this last night. I couldn't resist trying one this morning and they already taste divine!
That's great! Be warned, they're addictive. At least for me, an irredeemable brine-aholic.