Convert text to binary and the other way for any string input.
Convert text to hexadecimal and the other way for any string input.
Convert text to ascii and the other way for any string input.
Convert text to decimal and the other way for any string input.
Convert a number to written, spelled out words.
Get all the HTTP headers that an URL returns for a typical GET request.
Check if the URL is cached or not by Google.
Get details of any file type, such as the mime type or last edit date.
Get the gravatar.com globally recognized avatar for any email.
Make sure your passwords are good enough.