It seems no one else is willing to do this, so here goes...
In all situations where CAPTCHAs are involved, for users with at least 200 reputation, once a CAPTCHA is solved, another one will not appear for the next five minutes. Exceeding 40 minutes to submit a question, answer, or edit would previously trigger a CAPTCHA, but this has since been removed.
There is a limit of 50 questions within a rolling 30-day period and 6 questions within a rolling 24-hour period, including any questions asked within these periods later deleted; a question can only be posted once every 30 seconds, and users with less than 125 reputation are limited to one question every 20 minutes (source). Additionally, attempting to submit a question more than once every 60 seconds (for users with less than 10,000 reputation) or faster than 5 seconds after starting to ask will trigger a CAPTCHA.
Users with less than 125 reputation are limited to one answer every three minutes and cannot answer their own question within 8 hours of posting their question. There is no limit for users with at least 125 reputation, except that attempting to submit an answer more than once every 60 seconds (20 seconds for 10K users) or faster than 5 seconds after starting to answer will trigger a CAPTCHA.
Users must wait 15 minutes after asking a question to accept an answer and must wait 48 hours after the question was asked to accept their own answer.
Voting on posts
Normal users are limited to 30 votes (up or down) per day for all posts, plus 10 votes per day for questions only; the question-only votes cannot be used once the user has casted 25 votes on answers (source). Downvotes on posts that are later deleted do not count toward this limit.
Normal users are limited to 6 searches per minute. ♦Moderators are limited to 12 searches per minute. Source
Comments and comment votes
Users are limited to posting one comment every 5 seconds. Voting on comments, including deletion, is limited to once every 5 seconds. Fetching additional comments is limited to once every 2 seconds.
Editing and suggesting edits
Users are limited to editing five of their own posts per day. Unregistered users cannot suggest edits on posts less than 10 minutes old. Attempting to submit an edit more than once every 30 seconds (10 seconds for 10K users) or faster than 5 seconds after starting an edit will trigger a CAPTCHA.
Users are limited to deleting five of their own posts per day. Source
Showing upvote/downvote totals (1K privilege)
Users are limited to fetching upvote/downvote totals once per second. Source
Users are limited to changing their username once every 30 days; users with accounts less than 2 days old may freely change their name. Source