PSP Audioware's Xenon is my go-to mastering limiter and is loaded on my mastering DAW template. However, for mastering, I also use the following limiter options as well:
* Fabfilter Pro-L
* IK Multimedia Stealth Limiter
* Izotope Ozone 7 Maximizer
* Izotope Ozone 7 Vintage Limiter
* Magix sMax11 (Samplitude Pro X3 Suite)
* Voxengo Elephant 4
* Wave Arts FinalPlug 5