I have a pretty decent collection of Achievements on my profile if you click my name, above. The ones I know I am missing are the higher counts of Hours played (I have 250 icon; have seen 1K icon on your profile, maybe 2K or 4K on someone else's) and Number of people played with (I have the one for 50 people, have seen someone else with 250 people icon IIRC, maybe 500). There might be one for Artists who have uploaded-contributed to the Marketplace on here. I'm not sure of that one. The most unusual one I have is the bag of gold coins. This achievement is easy to obtain, simply buy something from the Marketplace, or give your GM a gift subscription. They have not released an official list AFIK. There is a thread somewhere in the forum, where a user was able to post most of them, shortly after Roll20 unveiled the Achievements feature. I think he made a Wiki page to show them but I forgot how to find that link. However a Mod or Dev replied and said they could not confirm the list was comprehensive, suggesting there were more achievements yet to be unlocked, which they were keeping secret.