I made a string bean, corn and tomato salad last week, which was an overwhelming success. Sure, the vegetables were farm fresh, but the hit of the salad was the dressing, which anyone can replicate at home.
All I did was cut up a ripe avocado and added it to the vegetables. I also added olive oil, fresh lemon juice, unrefined sea salt and fresh ground pepper before mixing everything together. The key is to use a ripe avocado, which will add luxuriant creaminess (helped by the olive oil) to the final product.
Don't only try this using string beans, corn and tomatoes; substitute vegetables (or beans, animal protein, etc.) freely. For a salad using lettuces, I recommend mixing the avocado in a bowl with the olive oil and other seasonings before combining with the greens; there's no reason to punish the delicate lettuces.