I never thought of Marmite and peanut butter! But, come to think of it, same sort of principle as satay sauce, yum.
PB hot chocolate sounds like a winner, too!
I like to make a sort of coleslaw (shredded cabbage, carrot, spring onion) with a simplified satay sauce (PB, soy sauce, lemon juice, garlic, chilli, ginger). On its own or mixed with Chinese or Japanese noodles; toasted sesame seeds on top won't go amiss either.
On a simpler PB theme: often, for breakfast, I slice up an apple and spread the slices thickly with PB (crunchy, of course). Fast, healthy, filling.