Looks like the full set is:
- reputation
- site-promotion
- questions
- tags
- comments
- badges
- answers
- search
- voting
- editing
- bounty
- user-interface
- specific-question
- accepted-answer
- markdown
- stackexchange
- community-wiki
- down-votes
- openid
- migration
- vote-to-close
- exact-duplicates
- etiquette
- notifications
- users
- closed-questions
- hyperlinks
- data-dump
- asking-questions
- recent-activity
- new-users
- profile-page
- flagging
- chat
- unanswered-questions
- retagging
- moderation
- data-explorer
- close-reasons
- user-accounts
- formatting
- interesting-tags
- up-votes
- meta
- statistics
- login
- rss
- favorites
- deleted-questions
- tagging
- votes
- tag-synonyms
- design
- featured
- community-ads
Plus, of course, the required and moderator-only tags. In addition to being pre-populated on the site, the list above is special in that none of those tags will ever be removed by the automatic cleanup logic.
