One of the most often used oils for making a vinaigrette salad dressing is cold pressed, extra-virgin olive oil. Unrefined grapeseed oil is another good choice for a vinaigrette, as are vegetable oils, including sunflower and canola oils.
If the dressing is for an Asian salad, sesame oil can be a good addition. This type of oil has a strong flavor however, so only small amounts are needed. Nut oils like hazelnut and almond can also be used, and add a rich flavor and aroma to vinaigrette dressings. These types of oils can be purchased at most supermarkets, though it may be a good idea to check out a specialty store for more high-quality oils.