Basic oil and vinegar: Two tablespoons olive oil, one tablespoon vinegar, tiny quantities of fresh ground salt and pepper, whisked together with a fork until it all looks thick and you can't see through it. (Any vinegar can work, with wine vinegars most classic for this. Use balsamic vinegar, get balsamic dressing)
Honey-Lemon: Two tablespoons olive oil, one tablespoon lemon juice, one half-tablespoon honey, whisked the same way.
Honey-Mustard: Two tablespoons mayonnaise, one teaspoon mustard, one teaspoon honey, and just a little lemon juice, whisked until completely mixed
Easy Russian: One tablespoon mayonnaise, one tablespoon ketchup, whisked until completely mixed.
Nice on greens that go on a sandwich or panini: one tablespoon olive oil, tiny quantities of fresh ground salt and pepper.