I'm sure there's a number of Hard Problems out there. I've got in mind a single one, but I'd love to hear any others.
The Hard Problem I'm referring to is consciousness. Specifically phenomenal consciousness (qualia), which I will abbreviate as PC.
To demonstrate, if you were to imagine a giant blue square, that square is part of phenomenal consciousness, anything else (e.g. brain chemistry) is not. As nowhere outside of phenomenal consciousness is there a giant blue square at that moment.
The Soft Problem is essentially what physical make-up correlates with what conscious experience (e.g. dopamine correlates with the experience of pleasure). Much leeway in that area has been made already, as it is merely measuring correlation. The Hard Problem is why anything is phenomenally conscious in the first place (e.g. why is there the experience of pleasure?).
To overly simplify the usual positions:-
Those that deny the existence of PC. Almost always by claiming it as an illusion, hallucination or delusion.
Those that claim a certain set of physical properties gives rise to PC. From Neural theories, to Quantum Mechanics, to Religious theories.
Those that claim there is only PC. Usually either idealists, who claim there is only the experience of the physical world, or panpsychists, who claim everything is conscious in some sense.
There are others, but most usually fit into one of those three categories.