I hate it when websites rot away; when huge fileservers disappear. Sometimes I grab copies just a few days before their last breath. Some are hosted under mirrors/ on this site, though I'm slowly moving them to a separate storage server, fs1:mirrors/.
(In particular, fs1:mirrors/rain/src.archive/ contains several gigabytes of IRC clients and servers.)
~ In October 2009, xkcd was temporarily redesigned to commemorate the final shutdown of the GeoCities web hosting service, killed off by Yahoo. Visit the mirror.
~ The Shoujo-Ai Archive fan-fiction website (2001–2014) is archived here and on fs1.
~ An untidy backup of Deviant Hearts fan-fiction site stored here.
~ In 2011, the Institute of Lithuanian Literature and Folklore published a free electronic textbook, Elektroninė lietuvių kalbos ir literatūros chrestomatija. Although meant to be freely available to high-school students, it used a proprietary Windows-only DRM mechanism. A day after release, several people managed to extract the raw PDF file, which is mirrored here (16 MB, original) and elsewhere (12 MB, minor edits).
~ Other people's file archives: SuperGlobalMegaCorp's VPSLand.