Ultra-compact nuclear rings (UCNRs) are ring-shaped star-forming regions around galactic nuclei that range in radius from a few to 200 pc. Only a handful are known in the literature, but thanks to the high resolution of HST, we are now able to study their frequency and properties in detail. We have discovered UCNRs in three nearby galaxies. In NGC 2985 we have found an intense ring of about 50 pc radius. In NGC 4800 we have found two rings, a patchy and intense ring of 130 pc radius and a faint one very close to the nucleus with a radius of 30 pc. These rings have probably been formed in connection with inner Lindblad resonances. In NGC 4579 we have found one sharply defined ring whose asymmetric morphology indicates that it is a resonance ring induced by a superposition of m=1 and m=2 perturbations. The rings we have found are important because they are tracers of the dynamics very close to the nuclei of their host galaxies. Only very few were known prior to this study and we have now virtually doubled the number of known UCNRs.