The Sample Slab is a standard reference for PCGS, NGC, ANACS, SEGS, and ICG sample slabs. Currently on the 2nd edition, this book features several hundred samples from the different grading services. Available as a PDF download, linked below.
If you would like to pay another way: please email me to discuss.
Note: this is a one time purchase, so if you accidentally lose the PDF after purchasing, just go ahead and download it again.