Extension Manager

Edit the alias list
Provides several automatic tagging functions
Adds autocomplete to search & tagging.
Turns BBCode into HTML
Provides query and selection-based bulk action support
Show a "down for maintenance" page
Allow users to favorite images
Bring a specific image to the users' attentions
Handle JPEG, PNG, GIF, WEBP, etc files
Ban IP addresses
Show various forms of link to each image, for copy & paste
Allow users to make comments on images
Show a list of uploaded posts
Allow users to rate images "safe", "questionable" or "explicit"
Allow users to send messages to eachother
Allows displaying a page with random posts
Do things with a random post
Regenerate a thumbnail image
Report posts as dupes/illegal/etc
This extension allows admins to resize images.
Allows admins to rotate images.
A simple wiki, for those who don't want the hugeness of mediawiki
Keep a record of source changes, and allows you to revert changes.
Show various bits of system information
Allow images to have tags assigned to them
Keep a record of tag changes, and allows you to revert changes.
Recount / Rename / Etc
Make some users only visible to themselves
Send PMs in response to certain events (eg post deletion)