Files that have been uploaded to hosting sites tend to have a short shelf life, but there are few that manage to keep them around indefinitely. In many cases, users will simply forget about a previously uploaded file, or have no more use for it. To help give these orphaned files a second life is FilesTube, a search engine that monitors files that have recently been uploaded to a handful of file-sharing sites and makes them easily searchable. While the files aren't in any way hosted to FilesTube, the service acts as a middleman to point you to where you can download them.
In addition to links that have been slurped up from FilesTube's search spiders, users can submit their own links. It supports seven popular upload and sharing services, and if users have shared something on their own server, they can simply drop in the direct URL and FilesTube does the rest.
Similar efforts to FilesTube have been constructed using larger search engines and their support of advanced operators. A few that have made the rounds earlier this year were SearchHacker and G2P; both make use of Google and are fully capable of pulling in a variety of file formats based on user-specified search queries.
Note: We're not down with piracy. These sites may contain illegally shared files, so use your head.