Some excellent ideas here and I like the scientific touch of Atgxtg. Snakes are a good example and one of my creatures is a snake, so I'll be looking at snake venoms to give me an idea for what to give it in terms of POT and damage.
For others, they're entirely fictional, lie my vamires, medusae and harpies (all of them potentially nasty). I'll look into LD50 and Agentorange's vampire rot idea to help guage my other venoms and toxins. One is a paralysis venom, so its damage should be pretty low as it's more a muscle relaxant, rather than muscle spasms, which can lead to respiratory failure. Maybe I should keep that in mind for cases of overdosing?
The medusa in my game, as mentioned, will have a venomous bite instead of the petrification gaze attack. My idea is that the venom will cause the cells in the body to become solid or calcify, giving them the stony appearance once it has fully done its work. So, am I right in saying it should be high POT and damage? When I think of it, it makes sense that it would be.