my favorite is one my Dad taught me when I was very young. It's easy to learn and easy to remember. it can be used in a variety of ways for almost everything. it works with string; cord; thin or think rope; on nylon or any material. I don't know the name but what you do:

fold a length of the end of the rope back on itself then tie that in a single knot making a tied loop at the end. there you go! with this simple loop in the end of the rope you can do just about anything with the rope.