Bring a large pot of lightly salted water to a boil. Add the pasta, and cook until tender, about 8 minutes. Drain, and rinse under cold water to cool.
Meanwhile, cook the bacon in a large deep skillet over medium-high heat until browned and crisp. Remove from the pan and drain on paper towels.
In a large bowl, stir together the Ranch dressing, onion, and tomatoes. Mix in the cooled pasta. Refrigerate for several hours or overnight. Crumble bacon over the top just before serving.
A yummy alternative to traditional pasta salad!