Censys is a search engine that allows computer scientists to ask questions about the devices and networks that compose the Internet. Driven by Internet-wide scanning, Censys lets researchers find specific hosts and create aggregate reports on how devices, websites, and certificates are configured and deployed.
FileWatcher is a ftp search engine which monitors more than 450 million files on more than 5,000 ftp servers. It allows you to search for files by specifying parts of the filename or other criteria.
SHODAN is a search engine that lets you find specific computers (routers, servers, etc.) using a variety of filters. Some have also described it as a public port scan directory or a search engine of banners.