Here are all the default Rails Mime Types:
"*/*" => :all
"text/plain" => :text
"text/html" => :html
"application/xhtml+xml" => :html
"text/javascript" => :js
"application/javascript" => :js
"application/x-javascript" => :js
"text/calendar" => :ics
"text/csv" => :csv
"application/xml" => :xml
"text/xml" => :xml
"application/x-xml" => :xml
"text/yaml" => :yaml
"application/x-yaml" => :yaml
"application/rss+xml" => :rss
"application/atom+xml" => :atom
"application/json" => :json
"text/x-json" => :json