My favorite knots to add to your list are adjustable grip hitch (AGH), siberian hitch, and zeppelin bend.
The AGH is super easy to tie and very versatile. The Siberian is useful for tying a rope around a static object such as a pole or a tree. Bends are rarely useful for me since I rarely need to join two ropes together, but if you are going to learn a bend, you might as well learn the most beautiful one.