One of the biggest issues I've seen with diets is from people opting for a salad and then dumping a big pile of sludgy ranch dressing on it. You might as well have dumped Crisco on it. And really, there's just no excuse for ranch anyway.
I do keep a bottle of salad dressing in the fridge at work, but it's only just there for emergencies. Really, there is no excuse for not making your own, and it's really, really simple to do. If you're gonna go through the hassle of making a salad for yourself, I can promise you that you can make your own salad dressing with even less effort than it took you to make the salad.
And if you make it to order for the salad you are making, you aren't stuck with a whole bottle of salad dressing you may not touch for awhile.
To make your own vinaigrette, just remember that it is 3 parts oil to 1 part acid. So you can use whatever oils or acid you like to make it, but that is what you need. For oils, I use extra virgin olive oil. If you prefer canola or something else, knock yourself out.
The acid is where I will vary. Sometimes I will use balsalmic vinegar, sometimes, a white or red wine vinegar and sometimes a champagne vinegar depending on my mood. If I am eating a salad and topping it with seafood, like shrimp or salmon, I will use lemon or lime juice as my acid instead of a vinegar.
The other vinaigrette addition to consider are the herbs. garlic, onion, shallots all work, nto to mention dried or fresh herbs. Whatever you have on hand. Personally, I am a fan of tarragon, so you may want to give that a try, as I think it has a really unique flavor.
Really, just try to tailor the flavors of your oils, acid, and herbs to the salad you're making, but I can assure you this is one of the easiest corners to cut and one of the easiest things to learn to do (and learn to like).