We have created a new, clean catalogue of ultraluminous X-ray sources (ULXs) selected by matching the 3XMM-DR4 release of the XMM-Newton Serendipitous Source Catalogue with the Third Reference Catalogue of Bright Galaxies. We remove sources in the centre of galaxies to avoid sample contamination by low-luminosity AGN, and also remove other known contaminants such as foreground stars, background QSOs, supernovae and supernova remnants. The sample is filtered further on the basis of XMM-Newton quality flags to ensure reliable fluxes and hardness ratios, making this the cleanest ULX catalogue to date. The catalogue contains 331 sources, 136 of which are unique to this sample. We present preliminary results on the collective properties of ULXs with respect to their host galaxy morphology, and research into individual sources of interest within the catalogue, including IMBH candidate M51 ULX-7 and a number of ultraluminous supersoft sources.