Caulerpa
Caulerpa is probably the most commonly seen macro-algae, at least in my experience. It is sold under several names depending on the species.
C. prolifera-Caulerpa, Blade grass, Blade Algae, Blade Caulerpa, Razor Grass, Razor Caulerpa, etc.
C. racemosa/C. lentillifera-Sea grapes, Grape...