I do not know of a list of the webhook payloads. The payloads are similar to what you see in the Discourse API documentation, but some fields are not included in the payload and in a few cases extra fields are added.
The easiest way I know of to see what gets sent in the payload is to configure a webhook on Discourse to point to http://example.com and then perform an action on the site to trigger the webhook. You can then see the payload by clicking the “Request” button from the webhook’s events list:
That screenshot is for a User Event webhook. You’ll see that the user’s email address is included in the payload.