GifCities: The Geocities Animated Gif Search Engine was a special project of the Internet Archive done as part of our 20th Anniversary to highlight and celebrate fun aspects of the amazing history of the web as represented in the web archive and the Wayback Machine. Geocities was an early web hosting service, started in 1994 and acquired by Yahoo in 1999, with which users could create their own custom websites. The platform hosted over 38 million user-built pages and was at one time the third most visited site on the web. In 2009, Yahoo announced it was closing down the service, at which point the Internet Archive attempted to archive as much of the content as possible. … Mining this collection, we extracted over 4,500,000 animated GIFs (1,600,000 unique images) and then used the filenames and directory path text to build a best-effort "full text" search engine. Each GIF also links back to the original Geocities page on which it was embedded (and some of these pages are even more awesome than the GIFs).
If you're just here for the under construction GIFs, here are all of them.