Like one suggested, in the veggie/salad section there is Marie's brand, which I like the Ranch one. It has half the calories as normal ranch due to them using yogurt. It also has mostly real items in the ingredients.
Other healthier options are Organic ones. If you have a Whole Foods or other organic stores or stores with organic sections, check them out. Not only can you find healthier salad dressings with drastically fewer calories, but they normally have real items in the ingredients.
I have only made one salad dressing in my life, but I hope to make others. One that I enjoy (some won't) is to take 3 Tablespoons of Extra Virgin Olive Oil, 1 teaspoon of hot sauce (like tabascoo or another brand), and the juice/zest of 1 lime. Mix those up and pour over salad. I tend to use less EVOO and more Lime juice & hot sauce because of the calories and I love hot sauce. The salad is also good with avacados, red onions and tomatoes. You can even make baked or grilled boneless/skinless chicken breasts for dinner and make sure to have left overs to put in your lunch salad.
Stay away from premade dressings with a lot of cane or artifical sugar. If you do not know the names of each kind of artificial sugar, then usually if the bottle says less sugar, no sugar, etc, then it probably has artifical sugar/sweeteners. Those sweetners are designed to make you addicted and thus, want more of the product as well as not get full. Also stay away from those with artifical dyes/colors. If you like strawberry jelly, there is zero reason for them to add red dye. Salad dressings do the same thing.