My four favorite easy ones are guacamole, good old onion soup mix dip, basic dill dip and a simple seasoned sour cream of my own. Guacamole and the classic soup mix dip you can easily find recipes for.
The easiest dill dip I do is equal parts mayo & sour cream with dill weed & onion powder- you can add a little zip with a squirt or two of hot sauce or a teaspoon of horseradish, or herb it up a bit more with celery seed and chives if you have 'em.
The seasoned sour cream is even simpler: sour cream, a couple splashes of Maggi seasoning (very handy stuff to have around the kitchen; it's great in sauces, dips, soups, gravy, and on vegetables & meats of many kinds, especially steak and chicken) and seasoned salt (I use Spike for this one, but you could also use a natural sea-salt-based one like Herbamare, or your regular Lawry's in a pinch, whatever you have around will work) and a little fresh ground black pepper. This is a really tasty dip that takes all of ninety seconds to whip up. It's also great on a baked potato, and so is the dill dip.