Dear student,
Water to start for naturally available and common liquids has a very high dielectric constant of 78.2, and some other chemical liquids like Formamide has an even higher dielectric constant of 111 and Hydrogen Cyanide has a dielectric constant of 114.9.Researchers have also found that a compound, Calcium Copper Titanate(CCTO) has a dielectric constant of over 10,000 so a molten or liquid state of it might also have a large enough dielectric constant if we're able to synthesise and measure it's dielectric constant.
Regards.