Since their discovery, Ultraluminous X-ray sources (ULXs) have attracted attention due to their combination of extreme luminosities and extra-nuclear locations. However, they are a fairly rare phenomenon, and attempts to investigate the general properties of the population have been hindered by a relative lack of known sources. Here, we present a large catalogue of ULX candidates including 655 detections of 475 discrete sources, based on the 2XMM Serendipitous Survey. To demonstrate the potential of such a resource, we present some scientific analysis of this population, including a general search for the spectral turnover seen, often at ~6keV, in the highest quality ULX data. We also demonstrate how the recent reflection and Comptonisation interpretations of this feature may be distinguished observationally in the future, specifically for NGC4517 ULX1, a previously unanalysed source with high quality data.