From what I've read, the only remaining candidates appear to be either sterile neutrinos or MOND (MOdified Newtonian Dynamics -- it does seem to keep changing.)
Did I miss anything else plausible?
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A plausible candidate is axions. These are (hypothetical) very light, very weakly-interacting particles, and notoriously difficult to actually detect. They are however well-motivated; they were first proposed as a solution to the 'strong CP' problem, and also arise automatically in string theory compactifications.
It has been argued that structure on subgalactic scales is incompatible with standard ideas about cold dark matter, and that instead it indicates "warm dark matter" made of particles with a mass of about 1 keV.
At the same time, there are possible observations of dark matter accumulating at scales of 10 GeV and >100 GeV, which is more in the usual range for CDM theories; but the data is a little complicated, and people are proposing models that are more complex than before - e.g. "A Theory of Dark Matter", in which there is a new force specific to dark matter, and "Double-Disk Dark Matter", in which most of the dark matter is a structureless, noninteracting halo, but a small fraction of it interacts and forms structures.
The logical combination of these ideas would be, that the dark matter is mostly a homogeneous cloud of stable keV-mass particles, with a subpopulation that interacts at the GeV scale. There are a number of models out there already, that have keV- and GeV-scale particles, but I don't see anything in the literature that really fits the preceding description. Apparently there hasn't been any crossover between "warm DM" and "interacting DM" research. But I bet it's coming.