• .htm - same as .html
• .json - ?? (in progress)
• .xml - ?? (in progress)
• .pdf - offers a pretty-printed PDF of the card (no menu or sidebar)
• .csv - see add csv file format
• .jpg, .gif, .png, etc. - just the image full size, i.e. ?size=full&layout=none
  if the file ending isn't the same format as how it's stored, convert?
• .rtf - Rich Text Format - http://ruby-rtf.rubyforge.org/ There's a 0.1 gem from 2005, http://ruby-rtf.rubyforge.org/docs/index.html The latest specification is 1.9.1 (2008), but it may make sense to implement an older one anyway, to avoid generating fiies that can't be opened with older software.
• Word processor formats:
  • .odt - Libre/OpenOffice
  • .doc, .docx - MS Word
• ?

see handle mp3 and other media types (.mp3, etc.)